That's really, really sad. And the worst part is, it's surely conscious on nobody's part. There have even been studies showing this effect. What's even sadder is that there's no obvious or easy way to fix it.
It's conscious on a lot of people's parts. I've also heard "no women, no sexual harassment suits" enough from people in tech to assume that there are a lot of bigots not dumb enough to admit it out loud. I could be going too far, though. Maybe the kind of dumb lockerroom overshare bluster amongst the employees and managers of sexually harassing companies and departments lends itself to admitting incriminating things…
Schools like to separate girls from boys, and points towards improved and safer environment. Conferences like to create women only sections, in the idea (with some irony) that it would improve gender equality, and like schools, make a better environment for teaching out technology.
I call it stupid because it fail some basic common sense. A mixed classroom, work space, or conference room is better because it increase cooperation, make society better, and switch the focus on the individual skill level rather than their sex. Schools have almost gone through this stage and fully gone over to mixed classrooms. The work space is learning the same lesson, but slower. As to conferences, I can only assume that they are looking at the workplace and fail to connect the dots.