ASICs aren't necessarily faster these days.
Some of that clock speed comes down to floor planning, which takes a lot of design hours, which ASIC project generally takes more design hours than FPGA anyway.
I am not in HFT so maybe not the best to answer, but ASICs just wouldn't work for HFT.
Basically FPGAs favour low volume, highly configurable projects. Whereas ASICs favour high volume, very defined projects.
Seeing as HFT algos must change often there would be great benefit in being able to reconfigure FPGA.
ASIC you would be stuck with your old HFT algos.
ASIC also are $$$ to produce an initial run, the initial run can also have bad HW bug in it which cannot be fixed and ASIC needs to be respun again, costing more $$$.
It works for Bitcoin, because people lots of small consumers would buy Bitcoin ASIC with simple and non changeable algo and because of the bottom line power usage mattered.
HFT firms I imagine don't care about performance per watt.
I am also not in HFT but wouldn't be surprised if there are also some timeless parts built as ASIC--perhaps not specially targetting HFT, but useful in that area)--and then just integrated via FPGA/CPU. Google's recently announced machine learning chip coming to mind.
