This is a perennial problem, even on these boards.
Which is weird, considering that I can't think of a single successful "serious" actual play...
I have a theory.
A lot of people have their identities wrapped up in their hobbies and fandoms. If that thing is not treated seriously and as a thing innately worthy of respect, are they?
I think this resounds doubly so with 'nerd activities.'
A lot of people into these activities spent ages 5 to 22-25 or so doing nerdy things* and getting direct validation** for it (grades, scores, access to the next level of that life journey, etc.). Come adulthood, and one gets significantly fewer gold stars for being 'such a bright young ______.' It's harder even to rate yourself -- there's no analog to 'taking [specific level of subject] two years early' when no one agrees on what you're supposed to have accomplished by 26 (or 40, or...).
*academics and associated secondary pursuits like math league or teaching themselves coding outside of class, etc., along with fandom in nerd-related media and IP.
**and while we all had at least one picked-on-for-being-a-nerd story, there were also always plenty of the important people who made clear what bright young kids/young adults we were, and how we were on the right track.
I'm a manager of a department at the intersection of computers, healthcare, and law (mostly programming). I have worked with a lot of incredibly bright people at the early stages of their adult life, and figuring out how to define 'am I doing well?' seems to be a consistent personal journey and challenge. And often they are fiercely protective of that thing (GPA, ACT/SAT/GRE* score, IQ, skipped a grade, taught themselves C++ in middle school, etc.) that used to be their defining victory.
*apologies to the non-USA readers. I tried to generalize this paragraph to not use our academic acronyms and it became an absolute mess.
And that's people who are doing those nerd-coded activities in their career. If you're a postal clerk or own a restaurant or are in marketing (or management...), you may well rate an 'N/A' on the previous scale of how you rated how you were doing in life.
For those reasons, I think a lot of people cling to their nerd-coded passions as evidence that they are, in fact, still one of the smart people. And thus are as fiercely protective of it as they are of those childhood victory metrics. Unless said nerd passion is comedy*, then laughing at it is an insult to that self-definition. So unless the game is inarguably silly**, including silly bits can be met with strong resistance.
*and even then, you are supposed to laugh at it the right way. And Life of Brian is actually the superior Monty Python film, or you're really supposed to prefer Black Adder, or similar self-defined rules.
**Tunnels and Trolls undoubtedly counts. Warhammer did, but sometimes the authors seemed to forget to make the satire clear and some people have grown up not viewing it through a dark comedy lens.
I've been slowly working on a Snarf-like Thread Post on the subject for ages. Kind of a side project to the 'No one is more horrible to nerds than other nerds trying to establish dominance/mark their territory' theory. They're both touchy subjects that could hurt feelings unless done absolutely perfectly, so they sit perpetually in the rough draft folder.