I'm not a heavy YouTube user, but I think I'm in a similar situation. If I am on YouTube I often want to read the comments (I have no moral problem with any of them), but if I'm searching for something on Google I don't usually want a bunch of spam/porn/whatever gets filtered by SafeSearch in the way of what I'm actually searching for. When I search I'm looking for something, and when I'm on YouTube I'm usually wasting time...they're very different use cases.