I would guess the reason you dont do it much on iphone is the lack of multitasking support.
Android alt tabbing has always been a basic part of life and now split screening is a thing too.
You lot getting widgets soon, maybe you'll get alt tab next year?
I understand it's a "hidden gesture" and thus all the UX complaints apply, but from pure observation most android users use the app switcher about as often as PC users use alt+tab... basically not as many as you think.
Most mobile phone users who are even slight technophobes will switch apps the old way from the home screen or app drawer. at least with the iPhone the "going home" behavior can accidentally surface the app switcher which after enough exposure might train such users to use it.
Idk, I kinda hate all the UX paradigms that android introduced, it often felt like they ignored much of what xerox parc taught as objectively good UX and tried to go it on their own, only to have to relearn all the same mistakes that Mac and Windows learned over the last 3 decades.
(ignoring everyone young enough to not remember that iphone first many years didn't have copy paste)
The iphone NEVER replaced a computer.
It replaced the television. No need for copy paste there.
The ipad is today trying, very shy, to hint at replacing a couple small use cases of the computer.
Remember the first iPhone? I wasn't into it, but a bunch of my (senior developer) colleagues were. I asked them how they lived without copy & paste and they all told me it was just no big deal.