Yeah, it's possible/probable that it was a dick move by some planning committee. But if I were wheelchair bound, I could imagine that being a) acknowledged and b) in the middle --- instead of always off to the side --- could be nice.
How many wheelchair users have backless chairs? Like, this isn't even a good design if it WAS actually intended for them. With that back part any wheelchair user would end up sitting slightly forward from the people sitting on the actual bench seat, possibly a good 6+ inches forward if it bumps into the handles on the back.