Admittedly, almost no one who is attracted by discussion of sports and celebrity meets community standards for rationality, most of us would find it difficult to include such references
I don't know ... there are plenty of references to people in comments in the style of celebrity fawning, just that they are niche celebrities instead of mainstream ones.
See this summary of rationality quotes - has fantasy author Terry Pratchett really said more rational quotable things than Einstein, Darwin, Descartes, Dennett, Jaynes, Aristotle and Sagan? Or is it just that people like him more?
Well, sort the same list [by karma votes] instead of number of quotes, and Pratchett moves up from 4th to 2nd.
That seems like either evidence that Pratchett and his fictional worlds have more relevance to rationality than the opening post wants to accept, or evidence that Pratchett is treated as a bit of a celebrity around here and your suggestion that people find it hard to throw in celebrity references isn't quite right, it's throwing in the right kind of celebrity references for people who celebrate vastly different properties in people which is hard.
I don't think the issue is Pratchett's rationality so much as his quotability.
Less Wrong is as a community extremely nerdy. That's true for almost any definition of "nerd" that captures anyone's intuition for the word. However, to a large extent, many aspects of nerdiness are not connected to rationality at all, even though nerdiness may be associated with more rationality in some limited aspects. For example, fantasy literature is probably not in any deep way connected to either intelligent or rational thinking except for historical reasons.
Yet LW is full of references to science fiction, fantasy literature, anime and D&D. In one recent example, a post started with an only marginally connected tidbit from Heinlein. Moreover, substantial subthreads have arisen bashing aspects of other subcultures. For example, see this subthread where multiple users discuss how spectator sports are "banal" and "pointless". I suspect that this attitude may be turning away not only non-nerds but even the somewhat nerdy who enjoy watching sports, and see it has harmless tribalist fun, not very different than friends arguing over whether Star Wars or Star Trek is superior which has about the same degree of actual value here.
There's a related issue which is a serious point about rationality and human cognition: Our hobbies are to a large extent functions of our specific upbringings and surrounding culture. That some people prefer one form of fantastic escapism involving imaginary spaceships isn't at some level very different than the escapism of watching some people throw and catch objects. Looking down on other people because of these sorts of preferences is unhelpful tribalism. It might feel good, and it might be fun, but it isn't helpful.