Many young people only have access to iOS devices for their gaming needs, so playing on iOS == playing Fortnite. Sure, if they had the option to play on a dedicated gaming device, many would prefer it, but many do not have access to the alternative.
Right but in that scenario their usage of Fortnite on iOS won't follow normal market behavior. e.g. a cash injection to the public (stimulus, etc) would result in a bunch of iOS players converting to PC/console.
Similarly, more than 0.07% of the population of the U.S. is incarcerated. That doesn't mean they want to be there.
I bet the phone players spend less in-game because their priority would be saving up for a console before buying a ton of v-bucks.
So the role of the phone client may be less as a cash cow directly, but more as an on-ramp to get people into the game on a device they already have, but they don't become spenders until they've graduated off of it.
Many young people only have access to iOS devices for their gaming needs, so playing on iOS == playing Fortnite. Sure, if they had the option to play on a dedicated gaming device, many would prefer it, but many do not have access to the alternative.