Two main reasons i see:

- poor testing between front and backend so that ppl don't know what versions of apps can work on that versions of apis, so forcing updates, "just to be safe"

- security slop - forcing the update of apps because they have an insecure library, like curl, so inane policy forces them to update...

You forgot the main one: it's just less work for the engineers and everyone else so they'll prefer such approach.

- increase "engagement"

- add after-sales revenue streams