To have a mobile app, you need a hardware and OS to run it on. You mobile has to connect to a network. Network is your cell provider. They are regulated. Cell protocol is owned by group of telcos, so is the infrastructure. Connecting to it uses radio, radio is regulated and licensed. It is also restricted what you can open for coding on a radio transmitting devices. In short, it a fucking nightmare to build a mobile device from scratch and have it open. And by nightmare, I mean impossible within legal bounds of international radio laws! 🐶🐾🫡