1. They don't exist, so if you own the game you still want it to work on your computer without maintenance updates
2. They still exist, so they don't want to have to update it every year because they can use that effort on making a new game and continuing to exist while still being able to sell from their existing catalogue because it still works
Either way it's in a game developer and gamers interest to have stable platforms
Yes, I can sort of understand Apple's argument that people should be running an email app that's been updated in the last 20 years, but I don't think it's defensible for software like games (or any offline productivity software, for that matter).
They've said that Rosetta 2 will stick around for games after it's phased out for other software, but it's hard to give much credence to that. Wouldn't be enough to make me want to bother publishing or buying games on Mac. They've dropped OS 9 compatibility (after having Classic), they dropped PowerPC support (after having Rosetta), they dropped x86 support after years of the OS supporting both 32 and 64 bit. And if they're keeping it available for games why not let me run other Intel Mac software?
Hard to imagine Rosetta 2 sticking around more than a couple years when Apple gets bored of supporting it.
1. They don't exist, so if you own the game you still want it to work on your computer without maintenance updates
2. They still exist, so they don't want to have to update it every year because they can use that effort on making a new game and continuing to exist while still being able to sell from their existing catalogue because it still works
Either way it's in a game developer and gamers interest to have stable platforms