Umm ... I don't know. I think the dynamic is a little different and has a lot of factors. It's not just about Lyme. For example, chronic "walking pneumonia" (chlamydia pneumonia or Cpn) is a "bad actor" in both FM and MS. There have been posts on the FM forun about Cpn and the topics was summarily pre-empted in the same way your Lyme post was. There's a lot to the Cpn thing, and anyone who hasn't been tested for that, mycoplasma and HHV6 probably should be. Some 60 - 70% of people with MS also have Cpn. Many have had MS symptons improve after treating the Cpn. I can give you the references if you want, or simply search on Wheldon (UK microbiologist so he's a researcher PhD and not a physician), MS, and Cpn.
So it's not about the particular disease.
People with chronic conditions have gone thru - hopefully - the grieving process. Having done that, they are at peace with their condition and don't want to deal with something else.
Comfort zones are comfort zones - even if they are bad ones. I think "battered wife syndrome" is an extreme example where people put up with really bad things rather than deal with change. Change is that fearful to some people.
People with chonic conditions get tired of being bombarded with "home remedies" and off-the-cuff diagnoses and treatments (My aunt cured her fibro with a taco diet etc etc)
Perhaps some mods come to view themselves as "experts" in their area. Like many in the medical community, they don't want to have their paradigm challenged. And no - I don't want to be a mod myself.
Plus there is some history on HW forums. We've had Lymies make posts on the other forums and they did it in a tactless, heavy-handed manner. We've worn out our welcome in many places. Last spring, we had one guy so bad that he not only alienated several other forums, but also the Lyme forum He was finally banned.
And relative to your post on the FM forum - yes - on the Lyme forum there is discussion of FM related topics and certainly chronic pain issues.
Lyme, anxitey, depression, chronic C. Pnuemoniae
"... expect the unexpected ..." (O. Wilde)
"I am an old man and have known a great many troubles, but most of them never happened." (Mark Twain)