Well, because the stock VW gearing was pretty much all done at about 80mph when the engine was cranking well over 4,000 rpm, the whole front of the car began to lift at about 70 mph making the steering squirrelly, the drum brakes would fade at your one and only panic stop (and you couldn't stop quickly after that) and it was making a whole lot of noise.
So the Judson would get you up to 70+ real fast - a real "between the stoplights" king, but it couldn't go much faster, anyway.