You are viewing the 3rd party clients as a negative. This was their greatest asset. Instead of destroying them, why not give them an SDK? If they put that SDK to show promoted tweets and other adverts in the stream, they could have sold far more inventory and still have all the metrics they need to show advertisers.

Instead, they destroyed them, destroyed the user growth they provided, destroyed the engagement they provided, and worse destroyed far more earnings potential they could have had if they instead just worked with all the clients to get the ad placements in there. They tried to copy Facebook and how they did things, but instead destroyed their most prized asset.