Pro/power user apps still cost a bit. Apps like Procreate and Luma sell for >$10 and seem to have great sales. I guess the issue comes when you have sold your app to almost everyone who is willing to buy it and then you are unable to make any more sales which forces you to either go to subscription model or to create a new listing "Procreate 2" to charge everyone again. Both of these options make people pretty upset though.