'Reconnect Automatically' is a pretty common user preference. However, so is using multiple computers. The change to certificates makes the latter slightly more cumbersome, but still worth it. However, if 'Reconnect Automatically' is set on one client machine, and another client machine attempts to log in as the same user, they end up in a forced disconnect/reconnect cycle (Machine A is logged in. Machine B connects, forces disconnect of Machine B. Machine A auto-reconnects, which forces disconnect of Machine B. Repeat ad nauseum).
If 'User Has Logged In Elsewhere' were a valid disconnect message, then the clients would be able to ignore automatic reconnection, and break the cycle.