I know it's unfair of me, but I'm imagining a default-dead early startup guy saying this while drinking the weird mushroom water, so thank you for that
female construction worker and FOSS hobbyist here.
I've been to tech conferences and do residential construction for a living. I'm a member of the local VFD. I'm familiar with predominantly male environments. I wish there were more women doing the things I love to do, but oh well.
Predominantly male environments are much more verbally and physically confrontational than mixed ones, in my experience. So my presence is really awkward. No one feels comfortable ripping on the new guy if the new guy is a new girl who's a bit shy. Sometimes the awkwardness dissipates, other times it doesn't. If it doesn't, I leave. So I suppose that this is one reason why predominantly male environments tend to stay that way.
It's always felt like more of a group dynamics thing than pointed sexism when I've experienced it.
One more thing: just because a job is physical doesn't mean that men are better at it. This attitude is extremely annoying to me as it directly affects my day-to-day life. I train 10-15 hours a week, and I'm stronger than the out-of-shape old guys. This doesn't matter. They know so many tricks to make the work go faster. Work smarter, you know?
I'm not sure if there's any data on female construction workers and danger/workplace accidents, but I'm actually confused by your assertion that men are better able to handle danger. Like, I don't understand what that even means.