Seems to me there are a lot of variables involved here. First off, are these clubs on-premise or off-? I've yet to attend, or even heard of (until now) an on-premise club that did not have plenty of swapping going on, at least here in Texas.
After all, how many people are going to be willing to pony up the kind of money the average on-premise club charges for admission and then not at least consider playing. Or if you are not looking to swap, then you are not swingers to start with, but just a couple who gets off on exhibitionism.
If it is an off-premise club with or without the ubiquitous "back room(s)", it may appear there is less swapping going on simply because there is really no safe place to play.
Another variable is whether or not you fit into the group in terms of the preferred age and attractiveness level (i.e., are you Barbie and Ken clones or not). First on-premise deal I ever attended we struck out utterly for just that reason; most of the attendees were twenty-and thirtysomething beautiful people types. Hell, we didn't even extrude on most of those people's consciousness, at least until we got into the hot tub, and the half dozen or so pretty people who were already in it promptly got out and stayed out until we got the message and left, after which they all promptly piled back in.
Something else that may have a bearing is people's fear of catching something in the way of an STD, particularly if they don't know you.
Or maybe there's just something in the water up Indiana and Illinois way...
-- Bear