A lot of it is due to peer pressure, marketing, and such.

I'm not from the US, but I knew people, who berated Android for having lower-end models (which meant even their flagship models are lower-end), some models still having headphone jacks (one of them screamed at me for buying a wired mouse, thus not insentivizing manufacturers to develop even better wireless technologies, thus enabling him to have a wireless audio interface and a portless Macbook (would be super elegant)), etc.

There's also Apple's massive foothold in the education market. I guess kids using iPads are more likely to stay with other Apple devices in the future.