Earlier quoted context omitted.
STEM hasn't made serious efforts to counter sexism? That starkly contrasts with my observations. For the entirety of my life (I'm over 25) that I can remember I've encountered programs and initiatives working towards getting women into STEM. All of the companies I've worked at instituted hiring policies that favor women (e.g. giving women 2 chances to pass a technical phone screen instead of one). And we're not alone…
These kinds of top-down initiatives are well and good, but the real problem is cultural. You only have to read this discussion to see why women don't want to work in STEM.
Furthermore, do you care to identify what in this discussion makes it so clear why women would not go into STEM?