They have these phones because they are cheap. Not because they've handled both iOS and Android and decided to go with Android. Come on now.
You can replace "cheap" by "much better value".
I used iOS and Android, and I wouldn't dream of having an iOS phone. I think the OS is just horrible.
The iOS notifications are awful. On Android they're superb. No comparison. And notifications are the most important thing on a smartphone.
The thought of swiping to one particular screen, starting the Settings app, selecting WiFi or Bluetooth every time I need to connect to something (which is very often), makes me nauseous. On Android you simply long-press the symbol in the drop-down.
The lack of the back button makes navigation all around clunkier.
The absolute need to use the steaming piece of crap that is iTunes every time I want to transfer music to my phone is enough to say never.
Then the hardware itself is crappy. They have a choice of a 4.7" screen, which is just too small today, or a 5.5" in a huge body. Not mentioning the blast from the past that is the SE.
I wouldn't buy an iPhone for just about any money. If the iPhone 7 would cost the same as the Nexus 5X, I'd get the latter with no regrets. Thankfully, there are a lot of good choices out there.