Their IP address could still be revoked by a hosting/server provider for violation of ToS (or any other reason). In addition to that, there's a lot of security

Their IP address could still be revoked by a hosting/server provider for violation of ToS (or any other reason). In addition to that, there's a lot of security and usability problems, like using TLS without a valid domain name, having the IP change over time, having websites impersonate them, etc. Instead, if they use a tor hidden service, it's must more difficult for a single entity to take them down.