What I don’t understand is why so many people insist that this must be the explanation, as if the current state of things is definitely a level playing field (or biased toward women) and the fact that there are so many more men in the field must therefore be due to something innate.

We’re only a few decades out from a time when women couldn’t open a bank account without their husband’s permission, and when raping a woman was perfectly legal as long as you were married to her. I think we should give it a little more time and effort before we declare that everything is now fair and any remaining discrepancies must be biological.

Or, like another commented suggested, maybe something about STEM appeals to men disproportionately.

If I had to guess, it's probably a combination of multiple factors. STEM isn't for everyone. But at a young age, more men are encouraged to pursue it. The high salary of tech jobs might attract men more than women, if men face more pressure to make a lot of money. Now you have a male dominated industry. And that starts to self perpetuate. Young boys see role models and women don't. Women outnumbered in male dominated workplaces become subject to more harassment. STEM starts to become a "man" thing, and less women feel like pursuing the career, especially when there are so many other occupations that seem more interesting. I think that's a plausible explanation for how we got to where we are today.

But nobody knows for sure. My point is, biology shouldn't be the default answer whenever we see gender gaps.