I might have worded that wrong. I WANT to run Windows 98 and Windows XP on these old PCs. It's part of the experience, and the reason I even bothered to put them together. If you've ever watched LGR, it's pretty much that kind of hobby.
Imagine you grew up in the 90s and at the languages school they had indigo and green G3 iMacs. Now that you're older and drunk in nostalgia, you hunt for one until, after years, you find it. It's green, beautiful, and it's all yours.
Now you want to use it to play games of the era. You purchase them on Steam, as opposed to just pirate them. Steam works on this G3 of yours, (just an example since Steam never worked on G3 iMacs, but you get the idea.) and you're able to play these old games as they were meant to be played, without issues.
Out of the blue, VALVE decides that Steam is just going to support the latest M-iMacs. The game and Steam are installed on your G3, but when you open the game, a pop-up appears reminding you that Steam isn't compatible with this iMac. You try to run the game out of the executable file but get the same results. You're effectively fucked, finding yourself crawling back to GOG, MyAbandonwaredotcom, your torrent site of choice, or your M2 iMac which have massive issues running these old games.
Niche case? Sure, but it still happens, and it's exactly what is going to happen to the current generation of game consoles in the future.