"Untapped market of engineers" yes it exists. The majority of my female friends with STEM degrees ended up as high school teachers. I had several older people suggest to me that teaching should be my preferred career choice because it was more flexible than a programming job (wtf...)

"every tech company would be taking advantage of it" - nope, no one is. I don't know why but my guess is its hard to admit you're doing hiring wrong, hard to hire people who think differently than you, etc.