Lots of cars use/benefit from subframe connectors. All the rustangs from the same era do. It's probably not anything specific against Mopars.
The problem is that with racing competitions people will do everything they can to exploit the rules. Give them an inch and they take a mile and see if they get caught during safety inspections. So the rules either have to be really specific and complicated, or just really simple and not allow certain things of any kind.
Plus all the rules come out of committee's for whatever organization is involved, and we all know how committee's work.
