There are a lot of European style cassette toilets in use in America. In campgrounds you see them mostly with trailers and truck campers. I've watched the routines those people go through to know I much prefer pulling up to a dump station and dumping through a hose. There is only one advantage I can see to a cassette toilet and that is you can park and not have to move to dump. That's a plus with a trailer. But then moving is why I bought a Class B.
I don't think in a Class B a dump toilet is all that restrictive in design. They have been located in Sprinters all up and down the driver's side perpendicular to the wall in back (LTV Free Spirit SS) to parallel to the wall all the way up front behind the driver (LTV Free Spirit) to passenger side up front parallel (RT RS Adventurous) to back perpendicular passenger side (Coach House Arriva). It is just more a matter of American preferences. Also campground infrastructure have almost universally accommodated driver side dumping at dump stations and camp sites.
Hey, but "grass is always greener"...