One criteria is if the server is reachable enough. Currently the monitoring system is happy if there are at least a few monitoring nodes that can reach the server, even if it is unreachable from most other places.
In one extreme case one server’s score was a solid 20, even if it was reachable only from usmci1-3strqkc. This server has since been deleted.
Some “big car company’s NTP servers” in the Philippines (222.127.1.18 - .27) are reachable only from at most a dozen monitoring nodes. Their official scores tend to be close to 20. My own NTP server in the Philippines can’t reach them. Maybe they’re only available to Globe networks (as that’s where they’re hosted) and a handful of others. Write your possible followups regarding this Philippine case to the linked thread, thanks.