I’m guessing this is to slow the Mopars down

You sure hit that nail on the head. Why doesn't NHRA throw some weight onto the GM cars in Pro Camero(Pro Stock). Maybe that will give the one or two Mustangs running a fighting chance. Also this would encourage a Dodge Challenger or two to show up.
.... b ecause they are perfectly happy with things the way they are. A few (VERY few) off brand cars, with no chance of winning, an a chevy in the winners circle every time.
Bottom line: more chevy racers, more chevy parts suppliers, more chevy fans, so more chevy wins equals more chevy fans in the seats, and spending money, and higher TV ratings.
Does anybody REALLY think NHRA is a non-profit? Hahahaha.