There are higher quality units and manufacturers who have looked a the issues with the standard TTs and designed around them.
Airstream is one example, the Casita and other shell types another. Lance, Arctic Fox, also get good reviews.
So why don't they dominate the market? Because the folks do not want to pay for the increase quality for what is basically a hobby or they do not want a unique design with limited options.
I have a $60.00 fly rod not a $1000.00 Orvis rod because it does what I want at a price I am willing to spend.
The fact that the majority are produced in the same area of the country, using the same materials and appliances, with roughly the same work force; speaks volumes.