I would say it is because of the tough fishing and the lack of larger fish. I fished both of the fall tournaments out there; your club tourney and the IMTT tourney. In the 1st tourney 3 fish were caught and the 2 day IMTT tourney 10 fish were caught out of 60 fisherman.
In total, I spent four weekends on Shelbyville this fall and I can say the fishing was very tough all but 1 day. Also, my boat partner got a nice 46"er the first weekend but of the other 8 fish we caught only 1 fish was over 40" and most of the other were low 30's. I believe this, along with the economic downturn, and expenses of travel, lodging, etc. is the blame.
Also, I believe your May tournament is scheduled for Saturday, May 21st? IMO a 1-day tournament should be held on Sunday. With a Saturday tournament, a potential angler would either a) have to take off work to pre-fish or b)go fish a tournament without pre-fishing. For a small time tournament I believe most people would not take off work, and I know I would never fish a tournament without any prefishing time.