I suspect it's because there's a large amount of people that started using smartphones before iphone blackberry and android existed. Eventually even non-smartphones had 3g video calls like almost everything had mms.

For those people who used an android, blackberry or android as their first phone more advanced than the ones designed for Africa and the developing world, which for some reason were insanely popular also in the US, they obviously don't miss what they've never had. In the US nobody else has 3g video calls either, so nobody misses it there at all.