Sure, the majority of mobile apps suck. But even then, 1% of it is still orders of magnitude larger than the number of "Linux" apps, and there are surely more actually decent mobile apps than that.
Besides, open-source doesn't have to be GNU, there are a bunch of open source apps on F-Droid.
Besides, open-source doesn't have to be GNU, there are a bunch of open source apps on F-Droid.