Yeah, I suppose this stuff isn't common-knowledge outside the commercial mobile development space.
There are complaints in this very thread about how shit the software selection is on the Play Store compared with iOS. This is why. Companies that have to, for whatever reason, pick only one platform to start on, usually pick iOS. If they add on Android later, they expect it not to make as much money as the iOS app, so may half-ass the port. In some cases, good apps that have enough revenue to keep them alive on iOS, may judge that an Android port won't be worth the added cost (especially smaller apps—think, one or two developer sorts of operations, they may run the numbers and project only a 20% revenue boost from adding an Android port, which may not be enough to cover the dev, testing, administrative, and support time the platform would require). There's a perception that, basically, Android users won't buy apps (which is... kinda true) and that's why the iOS version of an app might be ad-free and paid, while Android only gets an ad-supported variant—the vendor doesn't think creating and supporting a paid option on Android is worth the extra overhead.
I used to be a mobile developer, and I literally got death threats for charging $6 on Android. People just paid it on iOS and got on with using the app.
iOS is 15% of the mobile device market but generates 67% of the app revenue.