It's hard to know overall for Lemmy, but I know that both Lemmy.ca and Lemmy.nz have surveyed their members.

https://lemmy.ca/post/15125231 https://lemmy.nz/post/12001861

Both were around 87% men, where as this selfhosting one is like 96% men.

I would guess it's explained by society. Women are less likely to be in STEM which seems to almost be a prerequisite for Lemmy and possibly self-hosting, and of those women in STEM, and ( despite what you might think about your own house) there is still a societal expectation of them running the household and doing most of the household chores, even when they work full time. A third job, selfhosting, may be too much.