Please keep in mind that before you use the Strand server as an example, it isn't an Official map that comes with the game.. All though it is a 3rd party map, it IS in fact verypopular.. But I doubt even half of the players that own DoD:s even have it.. Maybe even less than that.
In my opinion it's amazing the server is full some times. I know it's popular because it is a near duplicate of the 1.3 map dod_charlie, which was a very popular map back in the day, but still. for a non official, non game packaged map, it does very well.. But don't ever expect that server to be full 24/7 like avalanche or Donner for example.. For the reasons I've already stated above.
Avalanche which is the only server I play on, is full.. No matter what time of the day. Even at 3 or 4 am eastern time I have had trouble joining up.