What are the mechanisms and why might they be important?

This paper is based on 3,600 college students over six years at a Dutch University. The question they are seeking to answer is whether there is an effect based on gender of randomly assigned student mentor. Entering students are randomly assigned to peer groups. Does gender balance of the assigned peer group make any difference on the major field of study the new student ends up choosing?

From The Effect of Peer Gender on Major Choice by Ulf Zölitz and Jan Feld. Abstract:

This paper investigates how the peer gender composition in university affects students' major choices and labor market outcomes. Women who are randomly assigned to more female peers become less likely to choose male-dominated majors, they end up in jobs where they work fewer hours and their wage grows at a slower rate. Men become more likely to choose male-dominated majors after having had more female peers, although their labor market outcomes are not affected. Our results suggest that the increasing female university enrollment over recent decades has paradoxically contributed to the occupational segregation among university graduates that persists in today’s labor market.

So yes, women assigned to peer groups with a disproportionate number of women are more less likely to end up pursuing STEM careers. Notably, men assigned to peer groups which are disproportionately female are more likely to pursue STEM careers. That is an intriguing asymmetry.

An interesting finding with an inordinate number of possible root causes. Why would women-dominated peer groups drive women towards more male-dominated degrees whereas the men in those groups respond by increasing their interest in STEM fields? And why don't male-dominated peer groups skew the decision-making process? The effect size is by no means determinative. Women in female dominated groups end up choosing female dominated majors at an only 8% increased rate; not determinative but still material.

The authors of the research are coming from a Social Justice perspective and so they are worried that more women in universities will drive women into female careers which, while more flexible and accommodating, are also less remunerative and powerful.

I am not particularly concerned about the consequences. Just interested as to what are the mechanisms and why might they be important?