Microsoft “turned it around” by extracting money out of its existing enterprise customer base. Apple had a base of fanatic customers even during its lowest point.
If Gmail is just email and I use it on my iPhone with the native mail application -- along with 5 other email accounts. If Gmail disappeared tomorrow, I would choose another email provider. There are very few "fanatics" for Android. It's the only alternative if you don't want to spend on an expensive phone. But the majority of people who can afford a more expensive phone -- buy an iPhone.