Income demographics are almost certainly part of it, sure. I expect iOS also makes users feel safer or more comfortable spending money than Android does, and that the average iOS device in the wild is generally more pleasant to use than the average Android device. There could also be age-related demographic factors contributing (that is, Android users may skew older, and older people might spend less on software, and may tend to use their devices far less than younger smartphone owners—this is just a guess, though)
Whatever the reasons, iOS device owners use their devices a lot more, and spend a lot more money through them, than Android users, on average.
> use their devices a lot more, and spend a lot more money through them
Dark patterns are the same, by any other name. I left MacOS because the squeeze got too rough, and didn't even consider iOS for daily use since it's file syncing options are a clown show. If Apple has reached this market position through unfair or anticompetitive means, I don't see why or how it would stop regulators from ruling in favor of competition.
I doubt you're right that Apple's more-strongly leveraging dark patterns (... do they?) is the reason iOS users use their devices more, and spend more money on them. There probably are several things that all contribute, but I doubt that particular one ranks in the top-10, assuming the effect even goes that direction at all, and I'd certainly not bet that it does.
I mean, hell, Apple goes out of their way to let you know how much you're using the device and where you're spending (or wasting) your time. And they make managing e.g. subscriptions dead easy. Sure seems counterproductive if the secret of their success is dark patterns tricking us into spending more time on the devices, and spending more money.
Whatever the reasons, iOS device owners use their devices a lot more, and spend a lot more money through them, than Android users, on average.