...
People usually get bored of the same old thing... and I am thinking that playing Quake4 online or UT2004 or whatever other "Insane LightSpeed shooter" is all the same thing...
So... as people get bored of the usual, they will move on to something with more of a challenge to it.. like ehhhh Red Orchestra.
tbh I loved to watch replays of best world duelist in UT2k4... my mouth stayed opened pretty often. You can hardly say it is always the same. It is same like F1 race... same track, same cars... but still you are watching performance that only few people can do... and at the end you will go play that game and try to do what you have just seen in replay.