Especially ~/AppData (and ~/Library) is problematic because the person uninstalling the app might not be the person who was previously using the app.

Reaching into another account‘s home directory to remove stuff feels very intrusive.

Which would mean that any uninstall trying to also clean out library data is going to be incomplete.

I think the consistent behavior of always keeping it is a win

I'd love if they'd clean up registry keys, or if windows did. But broadly I agree with you.

The user-specific parts of the registry are powered by files in the user‘s profile and ACLs do not normally allow other users to have access, so the same issue applies there too

lots of them leave crud in HKLM/System and HKLM/Software, as well as I think HKey_Curent_Config

I dont mind the per user settings crud, I do mind the system wide crud, because it can make reinstating the app to resolve an issue fraught, and I have to go manually find whatever opaque keys were set and remove them.

Some uninstallers do ask you if you wish to retain configuration clutter.