I'm pretty sure your estimate is wrong by at least several orders of magnitude. Lots of iPhone users also own MacBooks, for starters, and iPhone will nudge you to set backup when you connect it to any Mac. And of course they are going to be on the same Wi-Fi network most of the time, too, when that person is at home. I'm not sure how sleep plays into it exactly, but MacBooks do wake up on their own to do their backups and things like app updates, so I wouldn't be surprised if an iPhone can actually wake up a sleeping MacBook to back up to it.
So the only case that is relatively unusual is having the Mac back up to a local NAS, but that's only because NAS themselves are a power user thing. Still, turnkey ones like Synology etc are much more common than "triple digits worldwide", and if you have a Mac and a NAS, why wouldn't you set up Time Machine to backup to said NAS?
So the only case that is relatively unusual is having the Mac back up to a local NAS, but that's only because NAS themselves are a power user thing. Still, turnkey ones like Synology etc are much more common than "triple digits worldwide", and if you have a Mac and a NAS, why wouldn't you set up Time Machine to backup to said NAS?