Because some MBAs always want to double-dip: collect the premium fee and serve ads at that user.
Also, clearly defined APIs take a lot of flexibility away from them, which is yet another thing that beancounters don't want.
I dislike Reddit's narrative -- the Apollo dev himself is visibly gaslit by this one -- that the apps are "generating" API calls.
Nonsense.
Users generate API calls over client(s) of choice.
As soon as you understand that, you can apply first principles to the rest.