I can tell you why. In part, it's explicit sexism and goal keeping from men, sure. But a far bigger reason there are less women in tech?
Step into any engineering course at a 4 year university. Come back and tell me how many women where in your class. Get the picture?
Of COURSE there are less women in engineering jobs. They are less women in engineering classes! So while there are definitely sexism problems, far BIGGER issues exist with reforming gender roles CULTURALLY.
Women should be encouraged from a young age to pursue science if it interests them. They should not be given artificial leg ups to help balance a problem which will never go away without addressing the root cause.