There are cloud FPGAs, but they are offered as a compute accelerators, and have no access to the network. Trading FPGAs need network access for latency.
Im also sure that if theres enough customer demand (from people willing to spend $M), AWS will make network connected FPGA happen.
I'm sure they won't, at least without a lot of development. FPGA networking used for trading is borderline abusive of networking protocols, and I assume that Amazon doesn't want that on their production network.