Computing resources got cheaper so development didn't need to be as careful.

If one month you have $100 for food, but the next month you'll have $2000 are you still going to eat like you've got $100? Of course not!

But another part of the problem is that when development was slim you also weren't running very many things at once. I can remember writing different autoexec.bat and config.sys files to boot straight into whatever game I was going to play. Most to all of the resources were available.

Now we're constantly running a handful of things. The OS itself is huge, plus a browser that you haven't closed with a handful of tabs, plus the app for the store you bought the game from, and whatever else is in the background, and so on. So you feel the drag more because everything wants as many resources as it can grab before something else does.