This isnt really true. Banks dont pay anywhere near tech salaries. Its all lip service. The flow of good engineers is always banks -> tech companies and never tech companies -> banks.
I make significantly more at GS than I did at google. The difference is that the majority of my compensation comes from the yearly bonus - a quirk in finance.
My understanding is that I could get about 200k base at goldman and maybe a 20% bonus, this is for working in a high in demand field. Google/FB/Other job I can get 300k+ while working less hours, paid for lunch, better treatment, more respect.