You probably are thinking of other reasons Stu, and there are many, but I honestly think the primary reason is that some folks simply lose interest in the hobby ... not unlike similar experiences in several other hobbies.

There are tire-kickers who try it out and decide it's not for them. Some do not re-new for economical reasons. Some do not re-new for political reasons. Some simply took their ball and went home when others disagreed with them. Some thought that this hobby might have held some potential speculative financial rewards based on what a few high ticket chips have sold for on ebay. Some may have joined the club just to take advantage of a special offer that was posted in order to recruit new club members.... or as a result of a local interest news story published in a local newspaper or magazine. Some have sold their collection and do not have the same high level of "chip-fever" they were once afflicted with. We know for sure that some joined the club because they saw a huge potential for slabbing that they could take advantage of ... and were disappointed.

I'm sure that others have their own ideas why so many members drop out each year. What's yours?