Here it is: At 600 MHz, interference travels farther than it does at higher frequencies, all else equal.
The corollary to this, which you hear much more often from white space proponents, is that coverage extends farther at 600 MHz (better penetration of walls, etc.). The nice thing about that, they say, is fewer cells would be needed to provide, say, free Wi-Fi to a city. Fewer cells, however, mean more users are going to be sharing one access point. Each user will experience lower data rates as cell density decreases in a given area. Increase density, and they’ll interfere with each other more than they would on higher Wi-Fi frequencies.
This crucial engineering fact is why TV white space won’t provide for “Super Wi-Fi” nor “Wi-Fi on steroids,” for municipal Wi-Fi. For longer-distance rural links, those more of a point-to-point nature, I can see TV white space as part of a practical solution in some cases.