Money? You don't think Apple would make a killing on OSX licenses and lapdock sales if they allowed OSX on iPhone tomorrow?

Mac is a tiny slice of revenue for apple. OSX on iPhone would blow it out of the water. Apple would turn the PC market upside down, taking a sizeable chunk from Windows. As there'd be no point for most people to have a separate laptop/desktop at that point.

People also thought that phones needed keyboards before Apple showed them a better way. This is all on Apple to make a reality, no one else can bring general purpose computing to iPhone except them. It's their choice to make.