I've seen statements from users that it's not very useful. Those who sell can't even prove their huge earnings to see how profitable it is and it's also very expensive. If I have that app that is really working then I would not sell it to earn more because the app itself is already giving me continuous wealth.
It's not that simple - it does need some monitoring and tweaking, so if you are short of time with other things going on in your life I can perfectly understand wanting to sell it. And don't forget, given the rise of BTC, they'll always get back more fiat than they paid for it.