I think the number of them is the big problem.
Every few years new "backyard shop" starts making TC, they sell them and when warranty claims pile-up, they close the door.
For comparison Country Coach is the only big bus conversions manufacturer and they have rock-solid reputation for decades.
No TC manufacturer makes aluminium body.
I did own Airstream camper, I did own bus with stainless steel siding and I would love to own aluminium TC.
The only available are very old Avons and they come in too small sizes for me.
You'd think that with $80,000 pricing on new campers somebody would like to make lasting design?