Its not that Flyertalk hates trains, it's that the IP addresses associated with users on that shared train WiFi have previously been up to no good, and the reputational score for those IP addresses has been ranked as poor.

Flyertalk subscribes to a service where they choose to deny access to IP addresses that are a known source of troublemakers. This is in part because the security posture of the forum software is quite poor and the ability to defend against spam postings, and DDoS attacks is limited. So by blocking IP addresses of a poor or bad reputation they are looking to preserve the uptime of the site. Of course determined attacks will still prevail but it makes it more complicated for attackers as they have to use IP addresses of a higher reputation, which usually means more expense.