Hello, glad to see you back around here!
Part of it is it’s been “good enough” – we don’t use it internally on our hosting since we frequently rotate containers + images so our cadence is much different than what a self-hosting site would look like.
The other explanation here is between both launcher and docker, no system wants to take full responsibility for data removal schedule - the schedule for deleting user data should be in full control of the user.
I’ve run into some issues on self-hosted sites where cleanup also cleans up the new discourse base I needed to build, leading to a terrible chicken/egg problem. Having that not get noticed due to it being run automatically probably would be a bit of a snag to try and figure out.
A simple suggestion here could perhaps be to cronjob a docker system prune or launcher clean at your own risk. Could work?