The upgrades process for some apps almost necessitates that the those files/folders are decoupled from the app and can live on, as the app upgrade ends up deleting the existing app and dropping a new one in it's place.
I get wanting to keep user preferences around in spirit, but in practice keeping them forever can sometimes be problematic. If I tried an app, then installed it again in 8 years. I usually want to start over. For users who don't know about the ~/Library, this is hard. Especially now that Apple hides it in Finder.
When having issues with an app, deleting those files (or simply moving them somewhere else like the desktop as a test) is a great troubleshooting step to see if its an app problem or something corrupt in your settings or support files. When most users reinstall an app as a troubleshooting step, they aren't doing much of anything, with all those files sticking around.
UTM buries their VM disks away in a container inside the ~/Library. I have a 20GB disk in there. It's not always trivial small files. If someone deletes UTM and forgets to check for old VMs first, that's a big hit.
What I'd like to see is a something, maybe in the Settings app, that lists all the applications on the system and 3 options.
1. Remove Application, keep Library data 2. Remove Application and Library data (have it give into on what files are in there) 3. Remove Library data only (this could be used to refresh an app to start over with it)
Maybe in addition to that, as part of the Optimize Storage feature, it could crawl through all those old orphaned application support folders and containers, and list all the ones without an app installed, show the size, and the user can choose to get rid of them.
Looking at how much junk I have out there now, I may just do a re-install of my OS to clean things up soon. I usually wait for a new system, but this M1 Pro is lasting a long time. I recently migrated off 1Password and it seems to have a bunch of junk out there, including 4 year old weekly archives of all my passwords that it took for a few months for some reason. The files are encrypted, but who knows how long that will actually be good for.