I’ve run Supervised (/hass.io) for years in various locations and on a variety of machine types. It used to be the case that I could, and did, run any number of additional pieces of software, Docker containers and so on - the system worked, it didn’t break, I could update it, no silly messages telling me I’m being naughty for installing additional software.
The move towards making it almost impossible for a user to operate a Supervised system without these rediculous messages and being able to have control over their system is very obviously an attempt to get people off Supervised and onto something else, therefore dropping the reported users of Supervised and making it easier to remove it as an option. Last I checked, Supervised users had dropped from about 15% a few months ago to under 10%.
That being said, the compatibility of HA OS is now far better and in almost all cases a better option for new users who have an old PC or laptop knocking around they can use, so I don’t disagree with you.