Retracts were banded by rule when SPA was formed because they were expensive and complicated at the time(1991). The premise of SPA was to keep everything simple and cheap. No retracts. No pipes. No supercharging. Everyone ran side exhaust 61s. About 1995, 4 strokes were allowed because one of the principle clubs involved at the time got into a noise situation. Since then, 4 strokes have become dominant.

I've always maintained that anyone can be allowed to carry the weight penalty of retracts, they just can't fold them up in the air.