It would significantly reduce the number of pages someone has to flip through if we could filter by mature content only. We already have a filter that excludes mature content, but not one that excludes games with potential children in them. Personally, I never felt the urge to play a game that might have children in it and only applied to adult games, as I do not want to play with them at all if it's an option. I look for mature games only, and I always get disheartened when I see a really cool campaign promise that doesn't have the yellow label. On top of that, it's annoying to flip through 3-5 pages of games I would never apply to anyway just to find the ones that might be interesting.
Keep in mind that I don't think there's anything inherently wrong with adults who apply to non-adult games, but I do think that I am not alone in wanting such a filter option and preferring to play with other adults exclusively.