Because you are walking on eggshells for players who don't need to be walked on eggshells for. And it isn't helping them, and it isn't helping you. It is creating emotional distance between you. I think most games people don't want sexual assault, but spiders, halflings, gnomes and orphans are all viable subject matter for plot purposes and playing purposes in an RPG. And some of these games end up with really ridiculous lists of things to exclude. Which isn't just a matter of making the game worse because content isn't allowed, but it is also a tracking issue for the GM if you need to keep referring to a list of triggers for different people.