Lots of prop-trading firms aren't comfortable trading over the Internet. Often the concern isn't "someone might see my trades", since reverse engineering alpha

Lots of prop-trading firms aren't comfortable trading over the Internet. Often the concern isn't "someone might see my trades", since reverse engineering alpha from that is hard, or even latency, since not all strategies are super latency sensitive, ... but plain old infosec. These sorts of firms are super paranoid about the exfiltration of proprietary IP. When you add trading over the Internet in to the mix, you just have more ways to do that. You have highly dynamic cloud infrastructure to deal with (whereas traditionally everything is static), DNS security, tricky PKI/certificate management, the need for much tighter access controls, firewalling (both at the network and application protocol level) and the secure logging and monitoring of flow between networks. And everything needs to be tight enough so no single actor (external or internal) can compromise the system.