It is just design and marketing and figuring out what sells (i.e. dealer input).
I've never understood the concept of blocking the exits with beds but if you provide four forward bucket style seats with three point seatbelts you should sleep four or you are wasting a great deal of floor space if traveling as a single or pair most of the time.
Also, I've never understood the European concept of universally having two cramped side by side back seats. I socialize with many Class Bers and there is never entertaining inside the B. I think of it as more of a private master bedroom or tent if you must or just private space.
2015 Advanced RV Ocean One Mercedes Benz Sprinter
Previous Class Bs:
2011 Great West Van Legend Sprinter
2005 Pleasure-way Plateau TS Sprinter