Interesting thread but there might be something of a cultural bias there, in that the role of friendship in one's life is more formalized in some cultures than in others. For example, a formal friendship might be, "we meet once a week to have a cup of tea and discuss life for an hour or so". Some cultures in particular, I notice, are wary of what they might view as 'exploitative relationships' where 'leaning hard on a friendship for emotional support' can be seen as exceeding the bounds of what's considered polite and acceptable, regardless of the genders involved. It's something to keep in mind, anyway.
Outside that, it's worth thinking a bit about what happens when 'standard western' male-male friendships go sour, vs. when female-female friendships go sour. In the former it's stereotypical to think that men head-butt (anger and violence etc.) while women back-stab (nasty vicious gossip etc.). Men who've seen the worst of women-vs-women conflict and women who've seen the worst of men-vs-men conflict are probably the ones most reluctant to form friendships with the opposite sex. These are patriarchal stereotypes, true enough, but unfortunately rather common.
It's still possible to have solid mixed-gender friendships, but it has to be clear what the relationship is from the outset. A fair number of people (irrelevant of gender/orientation) use friendship as a 'testing the waters' kind of thing with an eye towards a relationship (which can go sour and not work out, or can turn into a lifelong bond), and some people are simply interested in a formalized friendship, often built around a shared personal or professional interest in something.
If only people would just communicate honestly about their intentions from the start. . .
P.S. Men who try to use friendship solely as a means to sex are creepy AF, these are the date rape types and the drug in your drink types. They also are likely to view rejection as a personal attack, and have major insecurity issues. Basically the worst kind of dishonest scumbag, avoid at all costs.