A lot of people forget that the major iPhone market (as far as Apple is concerned) is the US. The US market has fairly cheap plans (or had in the past) and subscribing to data storage is fairly simple.

Having all your stuff on one device that is easily stolen isn't  really a smart idea, but like most, I do it.

The other thing is that most people don't need a large amount of storage, to them it's primarily a phone, that's it. They don't need storage.

Then there is the next level of person that is a internet socialite that uses twitter, facebook, instagram etc that host all the data in the cloud, they too don't need storage.

Then there's the nerds like us that demand more storage so we can put all the stuff on our devices.

Yes I have an iOS device and yes I have owned Android as well. The first thing I did with the Android device is upgrade it's paltry 2GB storage to 8GB.
For a work phone that was fine, but for my personal device I had a 64GB iPhone 4s. And I had it almost full all the time.

My next phone will be the iPhone 7 (I currently have the 6 Plus 64GB version) and will most likely pay for the 128GB version this time.
I choose to do this because that is my choice.
Yes I find it annoying, but I prefer iOS over Android in what I do.