I also find the cut through, pass through, integration portal, whatever you wanna call it bizarre on brand new pickup truck based camper truck things.
Cutting a giant hole in the back of your brand new truck is obviously not really reversible, and in turn, basically destroying the resale value of said truck if you ever want to separate camper/truck and sell or upgrade one or the other.
Who is going to buy a truck with a giant hole in the back of it? Theres a small chance youd find someone wanting that, but a giant hole in the truck would be a deal breaker for most.
NOTE: Yeah, i am bitter about pass throughs because i'm too big and fat to fit through most of them. #dontjudgeme