In the 10 years I've been an android developer (ok 9) I've worked on maybe 15 or so android apps (for startups or large companies). I think more than half of those apps no longer exist or have completely changed since I worked on them - and one or two never even got released. But you know, I always got paid, so who cares? ;)

I do care a little about that to be fair, but one of the things I have learnt is that one developer (me) is only a small part of making a project a success. Even a mobile app often has a team people that contribute in important ways to its ultimate success, the business who is paying for it, the product owners, the analysts, the designers, the backend team, the clients devs.

All I can do is make my bit as good as it can be and try to positively effect the rest of the team (and hope we finish the app before the team ends up hating each other, the investor runs out of money, or the business changes strategic direction). So that's what I focus on, I can be proud of the code and the features we created, like I can be proud of completing a puzzle.

I do think you're right to be sceptical though, mobile apps are incredibly expensive! But businesses chasing customers spend lots of money to win (product development and marketing is also expensive) and if the core of your business depends on an app, well you better spend money on it, or give up.

One thing I do like about android is that it's not just apps, I've worked on an android based inflight entertainment system, and a payment system that operates in store kiosks, I've seen a fair few IoT and car technology related projects come up too.

But there's no particular reason to expand your development horizons in android's direction, you could also look at the server side? Sometimes when I look at contracting rates I think the amount of money you get paid seems to be inversely related to how interesting it is - maintaining a scala back end for a large financial institution seems pretty "well paid" lets put it that way ;)