Why no TT's that fully supports their own weight.

Needless complication it sounds like to me.

Plenty of folks tow "like a dream" overloaded payload wise with their half ton trucks. I was towing overloaded for three years and nothing bad happened. The only complaint I had was having the back suspension bottoming out now and then, causing the trailer tongue jack to drag on steep driveway aprons.

I happened to have the opportunity to upgrade to a bigger truck with more payload. I traded bells and whistles for more truck.