Hi Chuck,
My guess is the cutouts were only to save weight. I have a 1973
Italvega SuperSpeciale which has no BB cutouts and the 1974 Italvega
SuperLight did have cutouts. Both were top of the line for their year.
Usually there was a plastic liner inside but I agree with you why open
up the frame and bearings to moisture and dirt to save a few ounces.
Skip Magnuson
Spokane, WA USA