There are a lot of reasons why I don't choose Apple. I've done BlackBerry and Android, and have loved both experiences. Transferring ecosystems was slightly difficult but I adjusted, and I loved experiencing two different platforms. I'd even go to WP and probably will at some point, but I will never go to Apple. The following are my own subjective and biased reasons, and they are not intended to cause offense. Everyone is welcome to their own opinion! If you like Apple, great! These are just my views.
I dislike that Apple products are not only ferociously expensive (yes, I know BB and Android have expensive devices like the Priv and the Pixel, but Rogers often has Apple products retailing at over $1000 off-contract, and some of those devices aren't super new anymore), you have to buy Apple-related products to work with your iPhone. It's a money grab and I don't like it. You've already bought the brand, and yet they tell you you need to buy more accessories - which are more expensive than generic ones that should work with your phone, as they do with any other - in order for your phone to work with them.
The operating system is not my cup of tea. It's very simple (which isn't always a bad thing, but hear me out); which also means that there's no room for customization. You can't download launchers, you can't change the way the device looks, you can't have the same freedom as one could have with Android. I love customization and I change up my Android experience almost weekly in some way. I know that if I had an iPhone, I'd eventually go crazy because I can't change themes, launchers, icon packs, etc. Some launchers go so far as to totally change your experience of your device, and if Apple doesn't offer that, it won't hold interest for me.
I tend to steer clear of phones that are "popular" or that are seen as "status symbols" per societal standards. It seems like almost everyone has an iPhone. Some people simply buy it because "everyone has one," and I like going against trends. I like doing my own thing. I often grab last year's flagship or a phone that's awesome yet underrated because I want to be different and to have something unique. You pay big bucks for phones these days, and Apple is probably one of the most expensive mobile products you could buy - and don't forget the Apple accessories you need to purchase.
Another thing that keeps me going to Android: the freedom of manufacturer and choice. If you go Android, you have a ton of different manufacturers and options to choose from. You can choose a bigger or smaller phone - so, a Nexus 6P or Sony Compact device - or you can grab a phone with a sick camera, like pretty much any Samsung product out there; or maybe you want one with a removable battery and a literally big experience: the LG V20. You can also go the economical route and buy a midrange device that gets the job done just as well as a flagship device, but at a fraction of the cost: Asus Zenfone 2 or 3, OnePlus devices, or Honor devices. You literally have a tonnnage of options, and you don't need a pile of cash to make a decision.
And all of these phones look different! You can get a phone that is truly unique other than just a different colour. To me, all iPhones look the same (except for the Plus series, obviously!). You don't have as much choice when it comes to purchasing a new phone. With Android, yes, you may have a harder decision on your hands, but at least you have lots of options!
Don't get me wrong - I definitely respect Apple for their media reputation and for iMessage, which is one of the best messaging platforms ever. My boyfriend has an iPhone and I sometimes fiddle with it, but due to the reasons stated above, I know I couldn't use an iPhone for an extended period of time. Android is a freeing and more economical experience for me, and I've grown to love the stock Android experience as well. These are my reasons! Essay is done!