Only 5.3% of US welders are women. After years as a professor, I became one

I'm not the author, but there are a lot of motivations one could have. The less people are constrained by stereotypes and hostility, the more they can do what they want to do, the more likely they are to be able to make a living, the less they will be beset with self-doubt, the less they will be dominated and abused by others who have more opportunities. It's about freedom. Why shouldn't women be free to be welders if they want to be?

The more women are welders, the weaker the social constraints become against women being welders; or things like welders, because the stereotypes we're talking about aren't generally so narrow.

Women aren't a special case. Lots of people are hemmed in by stereotypes and biases. Why shouldn't they be free? Well, people who get the opportunities others are fenced out of do benefit from the biases, but that's not a noble motivation.