A web page is an Application/Human Interface. Outside of security concerns, companies can make more money if they control the Application/Human Interface, and reduce the risk of a middleman / broker extorting them for margins.

If I run a flight aggregator that has a majority of flight bookings, I can start charging 'rents' by allowing featured/sponsored listings to be promoted above the 'best' result, leading to a prisoner's dilemma where airlines should pay up to their margins to keep market share.

If an AI company becomes the default application human interface, they can do the same thing. Pay OpenAI tribute or be ended as a going concern.