Why are there so few blown small blocks?

I have seen one 6-71 blown 440 make passes at the race track, and NO roots blown small block Mopar.
The one blown 440 was singularly unimpressive. 11.80s at 3500 static altitude, if memory serves. Agree with PBR, most Roots on the street are eyewash. You can tell by looking at the blower pulleys. If the blower isn't overdriven 10%, it's loud eyewash.