Trailer construction quality question?

Much of it is probably the differance in materials used. Some brands use more MDF than a competitor. MDF is much heavier than plywood. Some use light weight composites, different models of appliances will have varying weights.

I change our bed platform from MDF to plywood and saved three or four pounds. The plywood is so much lighter that I had to swap out the gas assists, because the stock ones had to much pressure and the bed platform wouldn't stay closed.

If you research the same model TT over several model years you'll find weights change as newer and lighter materials are developed.