STEM is hard and it sucks.
Same reason women don’t have to mine coal. They have the luxury of being able to choose not to.
Men don’t have that luxury. We either earn or we live under a bridge eating food out of cans. Society puts an enormous pressure on men with the threat of homelessness and isolation, which doesn’t exist to anywhere near the same degree for women, because women have inherent value.
Men have no inherent value to society, their only value to society is realized through their work.
The result is men work harder and endure harder shittier jobs, including STEM.
If you want more women in STEM, then just eliminate all of their societal privileges, consider them inherently valueless like men, and put them under the same level of threat men are under of being isolated and going homeless.