Apple

With the younger generations, Apple was also smart to get into classrooms. They invested, donated or subsidized devices like iPads and computers so many of the current young people have grown up familiar with Apple and their operating systems.

Google attempted to do the same with Chromebooks, for example, but idk if you've ever heard first hand feedback about experiences with them, but all I've ever heard was NOT good.

The other point which has been mentioned many times is social media apps. That's how teens, at least in North America, largely communicate. Yes, arguably there are Android phones with better cameras and if you take an image or video with the native app and then upload it can be better but that's just simply not what teens want too or will do. The apps just work with great quality out of the box.

Not to mention app developers usually place an emphasis on developing their iOS apps before Android. Snap is a recent example where the CEO finally acknowledged that they had to do better with Android development.