The only think that would make wisdom teeth statistically less likely in births would be differential reproductive success based on having or not having them, like if they commonly got infected and killed people.

I'm not an expert, but it seems that if it doesn't confer a reproductive advantage a random mutation is more likely than not to eventually "break" the system and cause it to malfunction, and most likely to disable it. Sort of like how a lot of cave organisms lose their pigmentation after a number of generations, even though it's not evolutionarily (?) advantageous to be white versus their original pigmentation. Because wisdom teeth suck.