In the early days it was actually pretty normal to buy premium games (most pre-smartphone games were paid and I remember buying multiple games when I had an iPhone 3G), but as soon as people realized you could continuously milk people for subscriptions and microtransactions on a device they carry with them everywhere, it was all over. I'm sure there are still passionate devs making good mobile games, but that's not where the money's at.

Separately, premium apps are a lot more common on iOS to this day. I don't know if there's anything about the App Store that encourages this or it's just a quirk of history, but I figured it was worth noting.