Bad design. Drivers are coupled tightly with the kernel, and when component manufacturers stop releasing the binary blob for newer kernels, everyone is fucked. Google could've mandated requirements for releasing drivers longer or requiring open source drivers, but they did none of that... so here we are.

become so inconsistent

Your title implies that it was consistent at some point, but it wasn't. Android updates were never consistent. In fact, it's actually become more consistent in recent years, since the introduction of Project Treble. Most mainstream flagships now offer 4 years of updates, with some manufacturers even offering 5 years (Google and some Samsung flagships).

Bad control over the hardware. Android is 100% open source, but alas, not all drivers are. To be honest, it's by design of some manufacturers (Samsung for one, Mediatek is another) to keep drivers of hardware closed source so updating the OS of your particular Android based mobile OS lags hugely behind Android.

Android gets monthly security updates, which need to be included in the OS of the phone manufacturer. Lineage has weekly builds for their code which include the monthly security updates. Phone manufacturers are only required to 'supply updates for 2y after introduction of the model (not after end of sale), which requires them to give 1 upgrade (major version).

Alas, support for the wide variety of Android phones hinges now for 100% on the effort of the custom rom developers. For example: The 2011 Samsung Galaxy S2 has an unofficial Lineage 20 (Android 13).

To many devices running the same opensource software without the requirement to make the drivers open source.

Apple is completely closed, Microsoft has it's Windows closed with the option for hardware suppliers to supply the drivers (which need to be conform to their specs) Android is based on the Linux kernel, which would require hardware manufacturers that make drivers for the kernel to supply the drivers, but alas, as it's not a company, no methods to enforce this is available.

When you want consistent ANdroid updates, you need to either:

1. buy Google Pixel (Google is pretty consistent in updates)
2. buy a nice brand that offers 5y+ guarantee (include updates)
3. buy a device with active custom rom support, for example Lineage (worst case, you can update the device yourself as the code is available)

Qualcomm needs to maintain their drivers to make updates easy, but they usually do that for just a few years. Once they stop, updates usually stop as well because the smartphone manufacturers don't want to do qualcomm's work in addition to their own.

It's a major issue that hurts android as a whole and unfortunately there isn't an easy solution because qualcomm basically has a monopoly for high-end SoCs.

I see lots of confusion here. Android IS NOT Free/Open Source software, at least not the one you get with your phone. It's true that the bare bones OS is FOSS, but the same is true with iOS and Darwin. But they have a lot of proprietary crap on top of them.

The reason for offering a longer or shorter period of OS updates is a business decision, not a technical matter. There's at least one android phone (fairphone that I know of, not an ad or anything) with 7 years of updates, which is longer than the iPhone.

These arguments of costs of development and having to support hardware fall apart when you take into account that some smaller vendors are offering longer support than bigger ones like Samsung or hwawei, and when you look at which hardware they mount, it's basically the same. Same processors, very little variety in cameras and screens...

Of all the criticisms microsoft gets for being bloatware, one of its biggest boons is backeards compatibility and general support (after vista).

Its why the whole chromeos laptop fiasco is happening right now with "useless chromebooks"

It all boils down to the basic difference between the two Operating Systems.

Android, or rather The AOSP (the Android Open Source Project) is an open source operating system. That means that it's openly accessible to all, open to tinkering and tweaking. This is both the best and the worst part about Android.

Best, because it means people like you and I can create custom versions of Android if we want (look up custom ROMs). Plus we can look at the code and see if there's anything we like or don't like. It's great from a safety standpoint.

Worst, because this means that it needs to be optimised by manufacturers for each and every device they make. Since AOSP is a general OS, they need to make sure it works with the hardware in their device, with their camera and their processor. That takes considerable effort, although if they chose to focus on a select few devices every year, they'd be able to do so. However, given the race to sell as many phones as possible, it becomes clear why they don't update lower end devices (which is weird considering the fact that those lower end devices are the highest selling devices).

Windows, on the other hand, is a closed source operating system, meaning Microsoft makes the operating system and distributes it. It can be modified, and various drivers can be installed, but that's about it. That's also better and worse than Android.

Better, because it's kind of a one size fits all approach. They can push an update and the device manufacturers only have to make minor adjustments most of the time.

Worse, because if Microsoft screws up, the whole world is on fire. And you can only modify the OS, not see what it actually contains. Plus, unlike Android, Windows needs heavy modifications for any shape that's different from the regular. They messed up their Mobile OS platform (RIP WINDOWS PHONE) and while some laptops are experimenting with the form, like the dual screen Yoga Book or whatever, it's still very much a janky mess.

As a result, Android updates can be largely inconsistent. But that's not an issue with Android or Open Source Projects, rather the manufacturers who choose not to invest time into making it work. Hope that helps.

Edit: Reworded the comment to reduce the chance of misunderstanding.

It's not the carriers, it's the hardware. I think Windows support for old systems was really the outlier, and they are getting less willing. Security features, like chips with separate memory for keys, or other new hardware requirements can't always be filled in with backwards compatible software, and manufacturers choose which to include knowing the device will have a shorter or longer support life.

Like a lot of people already mentioned, it’s because of hardware driver’s mostly. But let’s not forget Microsoft has this figured out mostly already, since pretty much all drivers that have a version for Vista 64bit (2006) works on Windows 11.

Android is catching up a bit though, they split the update process and you now receive security updates almost directly from google since Android 10.

IMHO, you’re probably going to varying answers to this question. And I would argue that most of the barriers stem from Android’s greatest strength.

It’s open, it’s customizable, and hardware manufacturers have been given the room to set their own courses. Problem is, that extra wiggle room also creates more fragmentation.

Cause the brand of the phone decides how long it stays updated even if its running stock android. So lets say the average life of a Samsung is two - four years why support it longer when you can let it fall outta support to further create a need to upgrade.

Lots of roms let you run really modern android on old phones cause they put in the work. But a company turning a profit does really have a need to support phones for a long time.