You can make a platform because you want to sell it. You lock your platform because you don't want someone with a better browser or OS to compete with your lower quality products.

I think Valve is a good example of how to do it. Sure they also take a sizeable chunk out of sales, but they seem to compete on the same terms with their games with everyone else on Steam.

Going so far as to clearly make an unfair advantage doesn't make sense if your platform is already printing more money than you could reasonably spend. As is the case with Apple, and with Valve. Music sales are probably a drop in the ocean compared to what they make on hardware and the appstore overall. They just got greedy and started acting like assholes when it came to their competition.

> They just got greedy and started acting like assholes when it came to their competition.

I think we can all find examples when platforms were not "greedy" and eventually got pushed out as irrelevant. That's why Apple and others will try to leverage their position to promote their new services.

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.