Mining Mayhem is available on both desktop and mobile devices without downloading. There is no casino app or game specific app, period. Rather, like most developers, Carrot Gaming relies on modern technologies that allow you to play in the browser, which makes sense since the only casino it supplies is Stake which too is 100% browser-based.
This saves storage space, among other things. But most of all, it improves accessibility in an increasingly mobile world, where people expect the same experience instantly across devices.