It bypasses all proxies and interception, and hides all of the traffic contained in the tunnel. This means no traffic logging of the tunneled traffic, no IPS/IDS in front of the SSH service, and no visibility into the SSH traffic itself. If the box with the SSH service isn’t in a DMZ it also compromises network segmentation.

The problem isn’t SSH over TOR being insecure. It is sidestepping all of the security controls in place at your org and not talking to the netsec folks first.

Honestly I would be amazed if any competent netsec folks would even allow TOR outbound by default. I certainly wouldn’t allow it by default in an enterprise environment.