You think of 65" TV's as small? ...wha? Well, for most of us I'm going to assume that in their living rooms a 65" TV is plenty of screen, my 40" is good, I'd like to go to 60, but honestly anything more then that is just too much screen. I'm sitting approx 8 to 10 feet out from the screen, so anything larger is just not feasible in my mind.
My guess is that the TV companies don't feel its feasible to create such super-sized TV's for the average buyer. The weight and size start becomming serious logistical considerations once they start exceeding 70", if they haven't already at that point. By that, I mean transport, installation, etc.
Honestly though, if you want so much bigger my suggestion would be to move on to a projector. You can easily achieve over 100" at a very affordable budget, cheaper then your current beast of a TV.
This however brings up a sort of fine line between living rooms and home theatre rooms. The average consumer has living rooms, which is a space designed to be used not only for viewing movies and such entertainment, but social gatherings, drinking beer

, etc... Did I mention drinking beer?

Getting a TV exceeding 70" in that space, with a serious audio system redefines that living space into a home theatre space, at which point its going to lose some of that living spaciness.
Course, thats just my opinion of it.