Honestly I often know changes from Flighty for my flights before the airlines do or at least before they notify me. I had once my carrier said on time and Flighty said 90 mins delay. I went to the airport on time and turns out flight was delayed. Should have just trusted them!
But if, say, you are traveling with a pet that has to be verified at the counter, or you need to check a bag, the time windows for accepting those are set by the scheduled departure time. If your plane is still in the air or hasn't even left its origination airport (and, for the sake of argument here, we will assume you are flying from a smaller airport that doesn't have other aircraft that can easily be reassigned to your flight, so you know it will be delayed), it doesn't matter: they still close the check-in and baggage 45 minutes (on American; YMMV by airline) before scheduled departure. So you have no choice but to get there early and wait unless your airline actually declares the flight delayed when they know it will happen.
Not that many people on Android are willing to pay $60 for an app.
https://dontkillmyapp.com/ is just one example of the kind of problems app developers face on Android
Those platforms don't generate revenue
Like GP, I'm also a paid subscriber and I couldn't care less where else it's available. If anything, it being a native app rather than a multiplatform JS wrapper is a plus to me.
BTW, them being iOS-only means they're probably getting lots of marketing support from Apple and other perks. That can really help a startup.