Phones may have "very high reliability" (although I don't even agree that this is true, IME apps crash constantly, on my somewhat older phone, even the camera a

Phones may have "very high reliability" (although I don't even agree that this is true, IME apps crash constantly, on my somewhat older phone, even the camera app crashes sometimes) - but that's because they only have a single user. Try that with having to serve hundreds or thousands of users all over the world so that responses come back in a reasonable amount of time. There's things being done today in backend development that are probably overcomplicated, but Android is certainly not going to be the solution. And if your use case is really simple (e.g. personal hobby project and you're the only user), you can also just run some program from a single VPS, that's certainly very easy to do (and can be automated with all sorts of tools). For anyone new to backend development, I would anyway recommend to ignore docker and microservices and other such things at the beginning and just try to get a program to run on a single server (and having it being accessible from outside). All the other technologies build on top of this, and they exist for various reasons to make things more maintainable/scalable/secure, but they're not essential, in a strict sense, to backend development.