It is not about whether it is mainstream or not. Regardless of where you live, you can always buy a smartphone with the same features (or better) as the iPhone for a lower price, but yet people still buy iPhones.
The biggest reason is the exclusivity that Apple emphasises on. If you want to use the iOS, you have to buy the iPhone, and since every iPhone has a premium feel in terms of its finish and form factor, and because of the stability and fluidity of the iOS (which matter more to the average user, i.e. the majority, than specs), they have been able to position itself as a luxury brand within the the smartphone universe.
They have not compromised on quality by selling their software to every Tom, Dick & Harry, allowing even the low quality, laggy phones worth 5k to run Android.
It is not a question of right or wrong, but rather a case of two distinct business strategies. Google's strategy of diluting Android has given them a market share of over 80%, but the downside has been that their flagship phone is nowhere near as prominent as the iPhone simply because Android users are flooded with options.
Furthermore, you might get a bad impression of Android if you use it on a cheap phone, but that is never a risk with Apple because all of their phones are of pristine quality.
Apple's strategy has resulted in a premium brand image and intense brand loyalty compromising of users who value the exclusivity, but the downside of course has been the low market share.