They are exactly what they claim to be: specialists. You need to become one in some area that banks deem valuable. Current white-hot areas would be FPGA, machine learning (but you'll also want a PhD in statistics, or at the very least a good degree in it from a good uni) or be a badass systems developer who can write absurdly low latency code in terms of allocation, cache coherency, network sympathy and so on. To get this good, you need to have been doing it for a decade or more, so start now. At the bottom. No one leaves university and gets one of these jobs. They leave university, maybe get a PhD or work for a decade and work up to them. You are jealous of people who have put in thousands of hours of very hard work into their careers, but will you do the same?
Really, you just have to start trying to do it. Find an old, good hashmap library in C somewhere, benchmark it and then try to reach feature and performance parity yourself.
