That has nothing to do with what the majority inclinations are; most people who aren't interested in incest are going to see an incest-centric game and move on to one that isn't, instead of trying to get it converted to their tastes.Definitely the minority. How often do you see people ask for a patch that removes incest from an incest AVN?
Better comparison- if incest fans are the majority, why are only there only ~2600 games with the tag out of maybe 12000 (judging by a ubiquitous tag like "vaginal sex")? That only makes sense if the actual majority of adult game players is disinterested in or opposed to incest.
To be clear, I like incest games as much as anybody. But there's a real difference between a loud minority and an actual majority.