The thing is, most people don't need to be "productive" on their phone. I also like the idea of a big screen but in reality it's not all that great. Every time I use a big screen phone I wonder what it actually ads to the experience that compensates for the practical downsides (weight, looks ridiculous in your jeans (or doesn't even fit!) etc.).
And the fact that you can actually, comfortably, use an iPhone with one hand really IS a big plus. Try that with a 5" phone..
And I honestly question the premise that people really want those big phones. They only people I see with them are mostly tech junkies. People who want nice specs. If you want top specs with an Android you are forced into buying the huge screen models. A small screen Android phone with top specs would be, imho, a gigantic sales hit. So yeah, the big phones are somewhat of a self fulfilling prophecy.
Other people have iPhones or smaller android phones.
I couldn't agree with this more.