It's not docker itself. It's the mindset of some of its users: just throw in every garbage and don't bother about maintenance.

It's also often used by users shying away from maintenance -- often due to a demanding schedule. Sometimes not grasping the level of investment they need to do to have a good Dockerfile. If seen too many self-managed installations where the user mapping is utter crap an the process are running with random system users or random end-user UIDs.