If users wanted updates from Play Store, they would install the app from the Play Store.

There’s plenty of good reasons to transfer update ownership to the Play Store, too.

I’m interested, can you give a few examples?

Besides, it’s optional. Options are a good thing to have.

That’s true, until it’s not an option because a “bug” converts your apps to play store builds, and until this option gains a non-optional feature that nags you every x days to googlify your apps and expects that at some point you will either accept or misclick it. This is not something unheard of, play protect already does this.

There’s plenty of good reasons to transfer update ownership to the Play Store, too

Aside from self-hate or suicidal tendencies, I fail to see which.