The lists of servers for both Steam and in-game games (CSS, TF2, MW3, etc) are based on a list that is dynamically updated every time you open the Servers > tab; the Internet, very often however , for security reasons, limits the number of possible updates for each IP address. This means that if you update the list too often, the server will not respond and will timeout showing only a few servers or it will take a certain number of hours for the server to be added to the global list.
