I guarantee you somewhere in their backlog is an item that says "require app store for app installations on macOS"

This has been said for over a decade and it still hasn't happened, and Apple hasn't even tried to do so.

I think a better way to model their approach is to push non-technical users further and further away from the typical .dmg app installation approach, and put hoops up to prevent them from following malicious instructions, like the privacy/security and unverified developer hoops. Mildly annoying for technical users, but near impassable for the tech illiterate. We've been seeing this transition across windows and android for a long time, and it seems to be a net positive, if my family is anything to go by. I spend much less time on tech support now.