I dare say this hits it right on the nose, I remember well a long discussion on this very forum about whether it was appropriate for women to smoke a pipe, and several members vehemently saying that it was a male thing only.This is a debate on every forum that is "male dominated" that I have seen. Bass players. Tuba players. LS engines. Weaving...oh wait that was only male dominated until the 19th century.
Most of the time we males can be hostile in ways that we do not necessarily realize. (Complimenting looks rather than knowledge or, in this case pipes specifically with a direct reference to the gender of the smoker.) Make fun as you wish but often we don't realize how our "compliments" come across.
Finally, many have been run off due to private messages that are less than...dare I say it...gentlemanly.
Discussions about "manliness" help set a tone as well - "manliest" pipe shapes, tobaccos, "manly" poems, etc. People posting threads about being upset because they can't open carry into their favorite B&M. Et cetera, et cetera, ad infinitum. This forum often reeks of testosterone.
There were several women back in the old Yahoo Pipesmokers2 newsgroup who participated in the discussions. That place was a lot less testosterone fueled than this forum is. We also have a couple who are active in the PipesMagazine Facebook group. That FB group, however, is about pipes, tobacco, and accessories only.