I think it's a combination of the soccer fans being less interested in simulated sports and the actual soccer simulation being really quite shit. I can't get much out of it and I'm sure others are the same. Soccer's pretty difficult to measure performance in stats output too unlike afl. The aflsim is a bit rubbish too but it's far better in terms of the forum output, you can follow the game pretty easily plus the stats output is good.
Soccersim's activity nowadays pretty much all comes from one club anyway, which tends to not help things.
When I mean "big guns" I mean the guys that frequent the RL section. Also I quantified it as "as". The Sidhe crowd aren't the main part of the form anymore, and plenty of them are inactive or semi-active IIRC.
HGSS would be up there if it was a little more action packed. BBall > Cricsim > ARS > Daylight for mine.
lolno, soccersim is less popular because the sim is fucking shithouse. Anyhow BBallSim is easily the best.