This is something I wondered about too. I can only imagine they are hoping to sell enough cars to privateers to make it viable, or speculating some manufacturer with no internal motorsport department...
I think wrc27 spaceframe is quite close to Gr.B actually, only diffence is the 200 roadcars they had to build then. Sent fra min SM-S901B via Tapatalk

Because they're not the top Class, not competing with the big boys, which these 2027 Cars will be.
WRC mainclass from 2027