Another way to look at it is people are expressing a need to have a single good search tool rather than having to learn every individual site's search tool. Site hosted search varies wildly in quality too since many don't get much direct use (perhaps largely because most people uses general search tools like Google). I know I've built up a (usually unconscious) decision making bias that "search on site always sucks" that makes me shy away from them in. It feels like a reasonably rational decision to do so vs being garden-variety lazy.