English doesn't have a third-person gender-neutral pronoun and traditionally uses "he" when the gender is unknown, so it isn't really surprising that people, at least English speaking people, assume "male" until they know otherwise.

"They" and "Their" are perfectly acceptable as gender neutral pronouns. A stickler might object, but also bear in mind that in English there's no "proper" second person plural ...

You’re describing a historical norm, but it’s one I feel is rooted in a historical bias. Men ran the world and defined the word “man” to mean a person of any gender, but that was always an act by men. I’d like to see this kind of bias removed from our language, and it takes individual choice to make that so.

It's an easy trap to fall into. I'm looking around my office here and I can count about 20 men and 5 women. When I was in university the ratio far more male dominated. It's unfortunate that such an imbalance can make things uncomfortable for women (e.g. oafishly gendering things as male) in the industry sometimes.

Maybe because they don't pay attention! ;)