> Why couldn't they just add ads within the API

Because the first thing every 3rd party client will do is ignore the ads and not show them to users.

And 2 seconds after that, it'll be in the ToS that you can't do that. It's not like it will be hard for Twitter to check.

> It's not like it will be hard for Twitter to check.

Are you sure? That would require a centralized review and distribution process for all 3rd party clients, like the App Store for Twitter. It's not outside the realm of possibility, but there's very little incentive for them.

It barely needs to be more than a line in the ToS for the API. I'm sure Twitter already had a list of terms, and a way to ban people who misbehave. This is one more way to misbehave and get banned. Going right to an App Store would be insanity.

Showing ads isn’t enough. You need to count as impressions to bill advertisers and convince them to trust the impression data coming from third party clients.

They could just tell Apple & Google that your app doesn’t conform to their TOS, and poof, it’s gone. Especially PlayStore is really careful around 3rd party content.

> add ads within the API

Realistically, how much of the "content" is already ads? Ie corporate announcements, brand building, or political astroturfing, etc. It's almost like twitter is double dipping.

Without all the integrated tracking the ads would be basically worthless.