Rules organizations do all kinds of things for all kinds of reasons. Some good, some bad, some confusing, etc. As it was already mentioned, the point in this case was to keep the class evenly matched for relatively unmodified street cars- keeping out race prepped cars. Safer and stronger is great, but safer in this particular instance may also mean stiffer, which also means FASTER. So limiting the kinds of modifications also serves to slow the cars down. That particular class also has rules about what tire compounds can be run, which limits traction, which again limits speed. It's not a top end racing class, it's for owners of street cars to have some fun. Cars with more modifications, even if they are better ones, are kept out.