Historically, what happened was that there were riders trying to get championships. At the end, they were putting together loads of bikes to ride in all kinds of classes. Additionally, guys that were over 40 could do a race that riders under 40 could not do.
So, the rules were changed so that only the classes that "did not require specialized equipment" would be counted.
I still think it's kind of bogus. The overall championship should be limited to a certain number of races per rider, or something. At least give some a fair shot.
I can't afford nine classes a weekend. Anymore, you buy your number one plate.