BunkHouse RV's, why so many more TT, then Fifth wheels?

Because the biggest market for fivers is for couples who want a big house to live in full time, or at least several months at a time with seasonal moves.

If more families were looking for fivers for camping, you might find a shift toward less living space, more bunks. But the familes also need to be willing to pay the extra cost of building a big fiver, and as you say yourself, too much $$$$.