I am surprised there is so much money to be made in such simple applications. Kudos well done
I am learning Swift/swiftUI (as a backend guy with little previous experience with frontend/UI programs, okay) and building apps for OSX can be very painful. Starting from outdated docs (basically no books about OSX development since ... 10-15 years? or more?) to the new fancy ways of doing things with SwiftUI (that sells the promise that "you do it once,..." and it will work exactly as they planned to when you sell *Hello World* apps).
It's not the use case itself to be hard, but the fact you need to support multiple operating systems (which as you might know, Apple produces every year a brand new model, so imagine the fun), or that maybe the specific API you rely on (from Apple, not some random guy out there) has some weird memory leak because it's written in C++ or Obj-C, who knows last time someone touched it. And Apple is updating everything but that specific thing, so you need to build something around it. I don't even want to start on the lack of libraries for Swift - a lot of open source libs are outdated, bugged, last commits 1-2 years ago, which means you either have to fork and fix, or well, you do it yourself from scratch.
Nowadays selling software for OSX has basically nothing to do anymore with the idea or use case itself but all the toil that the poor developer has to put with up. I learnt that most apps on the App Store deserves some money (sometimes they ask for a lot, nothing to say, but that's their business model).