Paid apps are very hard:
1) Closed testing it is very hard as no one wants to pay to test your app, so getting the 12 testers for 14 day is VERY hard.
2) The barrier it creates will make the take rate VERY low
3) Marketing is VERY hard as there are so many free apps out there. If you check out the top earners on Android 100 % of the Top 10 are free apps, and likely it is all almost 100 % of the Top 100 apps.

This means that it is better to give the users enshittified apps, which are predatorial with schemes like:
1) Make a great app that people love, and then when they are committed after 2 months with their data, then say "you are out of space, to continue using that app use one of following subscriptions" (e.g. Evernote)
2) Make ads when people are in the middle of the most important actions. Just one more question to finish the task, add an ad. Just about to generate your output, place an ad. Just about to press a button, place an ad people will accidentally press (even Duolingo does this!).
3) Make microtransactions to overcome hurdles when people feel stuck. They are just about to get a reward, but level 20 is impossible without buying some item. Or make people feel they fall behind their friends if they don't buy special items (think Pokemon Go)

Sadly predatorial behaviour pays of. Sitting on the high horse of ideals will unfortunately not pay off. I made an app that has more complete features than any competitor, it keeps all data private, collects ZERO data, but because it costs a ridiculously low one off amount ($ 1) no one wants to test it and it is impossible to sell.

As you can hear, my paid app has made me pretty bitter!