Visible behaviour and functionality is changed or removed without user involvement, choice or recourse, turning every update into a game of Russian Roulette. Even LTS builds don't mean no breakage of behaviours users rely on.
From the developer's POV maintaining security/bugfix-only forks of every feature branch rapidly becomes intractable as a project gains complexity / matures. Meanwhile, for startups, "move fast and break things" is the creed. So as we demand more from our software overall, this situation can only get worse, not better.
The temptation for modern users to say "you know what? it's MY bloody computer, not yours; my problems are actually more important to me than whatever you think you're solving" and unplug from the update streams is overwhelming.