I believe the big manufacturers don't want to make a small phone (as other users have indicated) because of the big screen's addictiveness. Also, they can't fit a large battery in them so battery life would be a few hours with 1000mp 16k cameras.
I'd rather carry a 1" thick, 4" tall phone than a 0.3" thick 8" tall phone. No pants pockets look normal anymore, and it is even more awkward to walk with tight pants.