You'd expect more of these platforms would be all-too-eager to go into the API business.

Their value is what exists on the server side-- the networks, the content, the connections. The app is realistically more of a cost centre for them, and potentially an opportunity for friction or underserved use cases.

Opening the door for third parties would give them opportunities to expand their market for no additional cost.

For example, I could see Instacart integrations into smart-appliance platforms, thus fulfilling the long-wibbled-about premise of "what if your refrigerator knew you were out of eggs and would order more."