I think the difference here is that the "users who have private android phones"... Have private android phones! They use them for more than just work functions, so they're more used to them in general. I'd also guess that many of the people who are issued Apple work phones also have personal Android phones. That's actually kind of a detriment. I use Apple phones all the time, and Android and I are *not* friends. There are a lot of differences between the two brands and it takes me forever to figure out how to do things on Android when I have to use one. I expect the opposite is also true, if someone regularly uses Android then the Apple is a foreign land.
I don't think it's a case of either UI being objectively better than the other, I think it's a case of familiarity. The people who have private Android phones are used to them. The people who have work-issued Apple phones are not, and may even have to unlearn the Android way of operating.
(Tangentially, of course most users just stare at you when you tell them to factory reset before returning the phone. How many people have *ever* done a factory reset on their phone? For average users, at best they'll have done it once when they sold a used phone. For something done that infrequently you've got to give them explicit step-by-step instructions with 8x10 color glossy photographs with circles and arrows and a paragraph on the back of each one, explaining what each one is. Or better yet, just make it IT's first step when decomissioning a phone. Sure, it's better if the user wipes their data off first, but it's a lot easier than just expecting them to remember to do it.)