Thought we had had this out only recently?
I agree with Tom, Adam, Coddy, Mike, etc - it's a matter of a whole load of factors.
Personally I get about 4 pre ordained fishing trips a year - I elect for the 48 hr ('cos it;s the best chance to actually get some fishing in!) the Open (to support the club) Poole Cod comp (representing the club and small boats plus blowing the cobwebs away) and the flatfish/ray comp (well suited to our waters).
It's not the fishng of a monthly per se; although the format has been discussed - it's more the committment to fish the series competitively. I have always 'entered' the monthly comp if on the water, and reported my catch, but I could no more enter the wider commitment than I could enter a golf 'league' when expecting to play 4 games a year.
Adam is spot on, as reinforced by the other comments, the number of anglers in the club that are committed to anything beyond one off events hasn't changed. This doesn't necessarily represent any wider failing.