I think you wanted to say "because their hands are normal".
I've been told I have large hands and even I can't stand the 6, yet I know people with smallish hands who are happy. I think people's definitions of one handed use are different. On my 5, I can hold with one hand and get my thumb to touch the top of the screen along the whole top. No such luck with the 6, and with a case on, I suspect it would be worse. I'm also not interested in using reachablitly, which just makes everything more complex.