The things that yu can do with the Android Smartphones is ridiculous. There is an entire underworld of developers creating new operating sytsems that allow the Android phones to do all sorts of great things. You can’t do that with the iPhone.
The last thing in the world anybody is going to want to hear about is swapping operating systems in and out on a gadget.
Sure you can; it's called jailbreaking. There are huge numbers of apps available for jailbroken iPhones. The problem is that, as soon as you do it, you've opened your iPhone to vulnerability to malware just like a Windows PC or the Android phones.
Why wouldn't a selection of more than 350,000 available apps for the iPhone be enough?