Other than a handful of games where it does literally nothing but force you to sign in to something (such as Rockstar's Social Club shit or the Xbox Live for Windows thing from years past) most of the ones I see having a launcher just for the one game are ones that let you adjust settings before starting, choose a renderer version to use (Vulkan, DX11, or DX12, etc), or, like as is with Minecraft, allows you to have a safe modded version kept separate from your vanilla game or to manage saves.

You can also, in most cases, bypass those launchers by just launching the preferred executable in the game's installation directory.

Patch management

specific games like Minecraft I think it's nessicary, other games such as call of duty which insists on having one launcher manage all game installs I don't think is.

Imagine trying to handle all the different minecraft installs from the main screen, you would need to launch Java, load a Minecraft game, load a profile, close the game, open the game with the new profile settings and then hope it launches. This setup is very helpful, but I agree most games it is not helpful at all

The one big advantage I see with it is that you can have multiple versions of Minecraft installed at once, and launch whichever you like.

It usually makes it easier to centralize authentication. But more importantly (from the company's perspective), it gives the game producer a chance to upsell other products and micro-transaction content.

Minecraft is special. The launcher sets up a bunch of Java stuff and other game configurations. And it downloads updates and handles authentication. Technically you don't need it, but it makes it a little easier for the developers and the users. There are also third party launchers with additional functionality like downloading mods.

Other games often pretend they need that stuff when in reality they just want some more tracking that is not in the game itself.

To answer your third question about Minecraft specifically, you absolutely can run the Java version of Minecraft independently of the launcher. It's just a Java package. Find it and load it with your Java runtime from the command line and it'll play. Without authentication from the launcher, however, you will not be able to connect to Realms or indeed any multiplayer servers that have authentication enabled.

But for that reason, the Java version specifically of Minecraft is famously easy to pirate, provided you are fine with being limited to only playing locally or on pirate servers that have authentication disabled.

In the bad old days this was in fact the only way to play Minecraft in non-supported platforms (i.e. not Windows).

Managing updates, versions, mods, and settings can be done from a launcher instead of the game itself and it's often easier that way. If you wanted to adjust mods in-game you'd need to restart the game for changes to take effect.

Before Steam became the universal launcher, lots of games had their own. Minecraft isn't a Steam game so it comes with its own launcher.

With minecraft, it allows you to select from different versions and modes of the game and set up your account.

They do this and keep their top selling games exclusive to their platforms. Games like GTA have shown just how much money you can make off micro transactions. No company is going to just jump out of that market. They use their top games so they are more liley to get people to just have it installed. That way you install the launcher, put in your credit card, and you are only a click away from handing them some money.

There can be positive benefits though, auto updates, update news, community messaging or content.

But mostly so they can get the hardest part of selling done, a valid payment method input.

Allow you to set graphics preferences before launching a game, so you don't end up with a tiny 480p sized window on a 4K screen during an unskippable (and unrepeatable) first-launch cutscene; or the reverse, you only see the 1920x1080 (or smaller) cutout of the center of a 3840x2160 image.

I think the biggest thing is convenience. It's a lot easier for the launcher to do some handshakes and check/update to current patch. Other way is client opening, client closing, patch applied, client opens yet again, that type of deal

Not sure about Minecraft, but sometimes the launcher is simply there to make configuration, startup options, parameters, profile selection, etc. a smoother experience for the user. You can do this kind of stuff without a dedicated launcher, but some software publishers prefer to divide things up this way.

It's a dumb analogy, but I kind of think of it like restaurants. Some restaurants have a full wait staff with a maitre d, some have walk-up counter, some have a kiosk with a screen, etc.

If this is peeving you by the way, you can use multimc to create a shortcut, even to join a server or world directly to skip the title screen entirely

Now I'm wondering, Minecraft released 6 years after Steam. Why wasn't/isn't Minecraft on Steam while it's spinnoffs are?

Because it's coded like shit.

Minecraft is a fucking mess. 18 different products but 10 of them are just different platforms and the same game. All the authentication is different for the different versions too so if you have the Java one it doesnt work to login on the others.

Just shit software all around.

Other answers in thread are good, but I like them because I don't have to wait for a game to fully load if I misclick