But other apps are fairly easy to get people to pay for where privacy could be a key differentiator. Let's be honest, very few actually do give you privacy beyond maybe a couple of email providers. Spotify which people pay for to remove ads still winds up using data about you and almost surely selling profile information as a revenue stream. I don't know this for a fact so feel free to correct me, but I would be shocked if they didn't as most companies do today because charging $10-15/month is hard to build a large company off.
Yeah apps that collect super personal information (i.e security solutions, baby monitors) I can imagine privacy being key. But what about everyday apps like fitness trackers, journals, habit trackers and personal finance? From what I gather people complain about privacy of those apps but would rather go a manual route instead of paying for a private version of it.