There's plenty of smaller Android phones available too. But users clearly seem to like the bigger sizes, and frankly women seem to be a large driver. At least around here, most women I see have their phones - regardless of size - in their purse, and so they also seem to be very quick to adopt the large form factor phones. It's fairly common to see people with 6" phones here now.

But check out Aliexpress.com, and you will find lots of small form factors, if you're ok with ordering direct from China.