Yes, the incentives are often perverse. However, there are many reasons to build a platform even if your endgame is not extracting all of the value yourself and that is, make money from the commission on the platform or protect your interest in other businesses through the platform(for example, Android and Chrome platforms protect Google from being pushed out of data collection for advertisement).

Anyway, businesses might have that kind of aspirations but thats why we have governments. An important argument against influence of the businesses in the government and libertarianism.