This is a valid question - you may be seeing more fungus in QT because you don't have any bottom feeders in there to eat the food quickly. What kind of filtration do you have on the QT?
The QT tank for my bettas is a 2.5 gallon mini-bow with the Whisper internal filter. I have the filter on the lowest setting for the bettas. I usually get a white, cottony-cloudy looking substance on the bottom of the tank. This substance forms around the fish waste and any uneaten food. I use a turkey baster to remove this cottony stuff every day that the fish is in QT.
IME this is not unusual in a QT tank, since in QT we often don't have the same filtration or tankmates as the main tank. Use your vac or a turkey baster to remove the fungus whenever you see it.