As far I understand it, FPGAs are used in trading for their low-latency response. It is hard to respond in software much faster than 5 us, even using kernel bypass, etc.
They're not implicitly low latency though. FPGAs are about having the control and resources to structure workloads to complete in a minimum number of clock cycles. It's not an automatic thing you get by cross-compiling a C program onto a different platform.