But that, again, is a secondary issue relating to a host of things like marketing, whether there's any profit in it, etc.
I disagree. The lack of availability reflects that developers do not feel there can ever be a market given the fragmented and somewhat random evolution of unix based OS families.
Of course, but whatever the reasons might be, the reality is that non-vendor Unix (Linux, that is) is a failure in the consumer market, while vendor Unix coupled with a specific GUI and App Server/VM environment (iOS, OS X, Android) work pretty well and have a huge number of applications written for them.
I just remembered a joke a friend told me a few years ago: