<< Why do NASA not know how to have fun? Sigh >>
I suspect it's because they've learned a hard lesson, one that most public-facing organisations learn sooner or later: a sense of fun is a dangerous thing when you're dealing with the public at large. If I suffer from an abject lack of sense of humour, a significant part of that is down to years spent in a job involving talking to the public.
I don't know if you recall a certain incident in the 1970s, when NASA released a certain photograph with a certain geographical (all right, areographical, if you insist) feature on it that looked a little bit like a face? NASA probably thought, "oh, cool - look: a rock that looks like a face; isn't that groovy?" (I'm paraphrasing - it was the 70s.)
NASA must have learned pretty quickly after that that you have to be enormously careful about what you say and what you suggest. Show a sense of fun, or any kind of emotional investment in what you're doing, and the public will take indignant offence; or they'll mock you for your stupidity (and "it was just a joke" doesn't ring true even when it's true); or they'll misrepresent whatever you said and construct unconvincing yet elaborate conspiracy theories about it, with websites and everything.