About too much tire…
I wonder why Lemans cars and the kind use skinny tires… Just kidding…
Its all about balance, suspension, alignment, power, weight, track and the list goes on and on.
Sure a 275 tire on a 8" wheel wont be used to its full potential on some cases. however it will still perform better than the 225 on most cases; especially autocross. It will act like a motorcycle tire… as camber changes there is always part of the tire in contact… For example: with a square 225 tire, the moment a major camber change happens, the less of the tire will be in contact with the ground.
Many professional racing teams are limited by rules as to the tire width and compounds they can use.