How did you see only around 200..220 are working ?
Probing the MN list: If host online + Port 9999 open => MN active.
Most down/inactive/unreachble MNs are from Amazon IPs.
---> Some folks aka MN admins, didn't assigned static IPs for (aka "Elastic IPs" in Amazon speech) for their AWS instances.
---> When Amazon changes IPs these MNs arent reachable anymore under the MN IP they are listed in MN list or "known in the DarkCoin network".