I'd say the existing app stores plugged on distribution repos (apt) provide a very large amount of free software, thus reducing the incentive to look for paid

I'd say the existing app stores plugged on distribution repos (apt) provide a very large amount of free software, thus reducing the incentive to look for paid software. For the seller, being able to sell is one thing, having to run software in a tiny and extremely fragmented market (a large bunch of slightly different distros) is another one. Then osx happened, and the linux desktop never happened.