I can play EA sports games online using my PS2 but I can't connect to play other PS2 Online Games. Why?

Specifically, it appears that the games I am trying to connect with online use the Gamespy Network. Does this network require me to do something other than the general network configuration? Stumped.

It's more than likely that those companies have stopped supporting online play for those games.

Sony lets the game's company run their own online server, so if the company stops supporting it, then that game won't have online play anymore.