Well you see, finding a way to reliably deliver ads via the API would have taken far too much developer brainpower for a company that can’t make a functional video player or a mobile app
It honestly wouldn’t be that hard at all. You deliver ads via the API alongside actual posts, as if they are an actual post, and forbid altering them in the developer ToS. If you want to be anal about enforcement, run popular 3rd-party apps in an emulator to verify that the JSON returned by the site is unaltered when it’s rendered in the app. You could put this together in a weekend.
Which really just speaks to quality of talent at reddit, or the management at reddit suppressing that talent. Or both.
I’m pretty sure the real issue is the data collection Reddit wants about user habits. They can’t get thst from 3rd party apps, even if they make browsing habit data (scroll speeds, post linger time, ads displayed, etc) a mandatory part of the API they cannot verify what the 3rd party app is reporting and it becomes junk data that advertisers cannot rely on. They need complete ecosystem control to make the marketing optimizers happy. So, fuck the consumer!