At this point in time, I really don't think that the situation is based on a lack of twitch-shooters, but rather the casual gamer's interests based on graphics and accessibility.
Back then, you had your two crowds: Quake/ UT vs CS. Not to downplay CS at all, but many casual players I knew were really into it. I only knew one person that was into Quake (namely, 3), but he eventually sold his soul to WoW.
With that said, that same "casual' crowd seems to have moved on to the CoD 'wagon. Like Apple, it has become a fad of some sort; the COOL game to play, thus the dying breed of arena-style players.
Now we have a bunch of FREE, amateur-made games (Warsow, etc.), which seem to be dying a slow, painful death as well.
As much as I love BC2, my sanity from holding SPRINT down can only last so long. The art of movement and precision aiming will be soon forgotten, I'm afraid.