The reason why you aren't given an infinite, or multiple, points of creating your own UX entry points is because that means the entire platform has to be built using all of those points - most of which cannot be analyzed, tested, nor skillfully given to developers in UX docs so that they make apps which conform to whatever *you* design for them.

Its not impossible, just unrealistic to have a stable platform with a tightly constrained physical environment on even more tightly constrained resources to do that. For laptop/desktop paradigm, sure. Not for mobile(-first) devices.