Well the thing is, for it to be viable for the average person it would need to be able to suit a lot of different use cases. A lot of systems and infrastructure would need to be built up as well, likely to the point where it starts to resemble currently available typical phone OSs. There would need to be consistency and some amount of stability in terms of APIs and such for app developers to use. Having fragmentation of the ecosystem (different distros), with low level differences (compared to just a manufacturer or carrier skin+apps), means that it will be more difficult for app developers to target all platforms.

So to some extent, I guess it is partly due to a lack of momentum, however it is impossible to ignore the extent to which the Linux way of doing things is going to hinder adoption.

And don’t forget that the Linux ecosystem has a habit of competing against itself for the little marketshare it does have. The fragmentation of the ecosystem also leads to work being done many times over for each distro. It makes it very hard for Linux to catch up and keep pace with the likes of Android and IOS.

I am not hating on Linux by any means, just being realistic about the situation.