My son-in-law builds custom homes 5000 sq/ft is small by his standards. What his customers call junk and shoddy workmanship is a far cry from what I call junk.
The point is you build what the market will accept. If it works, does not fall apart and "looks good", people do not care if you used a claw hammer instead of a chisel to fit two pieces of wood.
There are some well built, house spec. trailers out there but they are heavy, small and expensive.
The biggest consumer complaint is not how they are built but the fact that parts do not work or break to easily. If the TT meets the customers expectations, it does not matter how much spit and bailing wire was used in the construction.
This is sad but true and not likely to change soon.