I think it's more useful to think in context of vertical integration. Mobile phone software is very tightly vertically integrated such that a single company can

I think it's more useful to think in context of vertical integration. Mobile phone software is very tightly vertically integrated such that a single company can control components that historically other companies were able to compete at providing. Apple and Google not only control hardware, kernel, OS facilities, user land, software loading/download facilities, but also payments, code signing, and even venture into other forms of banking. On top of that, they're actively blocking potential competitors to many (most) of those pieces.