That's a good hypothesis but it looks like at least some seed servers are listening properly:

ubuntu@hive-node-0:~/hive-docker/data/witness_node_data_dir$ telnet hive-seed.arcange.eu 2001
Trying 91.183.35.138...
Connected to hive-seed.arcange.eu.
Escape character is '^]'.
1(����bHW<�jg�]W���\fhUS��u^]
telnet> q
Connection closed.
ubuntu@hive-node-0:~/hive-docker/data/witness_node_data_dir$ telnet hived.splinterlands.com 2001
Trying 65.21.199.174...
telnet: Unable to connect to remote host: Connection refused
ubuntu@hive-node-0:~/hive-docker/data/witness_node_data_dir$ telnet node.mahdiyari.info 2001
Trying 95.216.40.109...
Connected to node.mahdiyari.info.
Escape character is '^]'.
O,�:Di�0T��'�4�e��Z��mäT%�^]
telnet> q
Connection closed.
ubuntu@hive-node-0:~/hive-docker/data/witness_node_data_dir$