Used to be small local gunshows were a way for "basement" FFLs to sell some guns and make a little cash. Because they had little overhead they could sell for less than the brick and mortar stores, one reason "good deals" were more common. They spent every weekend in another small town sitting behind their table. Now, those same FFLs can just be an approved FFL for several online sellers, and make just as much staying at home as they did tromping all over the country years ago. Instead of giving up their weekend, the customer makes an appointment when it's convenient for the FFL, to come and get the firearm they ordered. Also used to be there were not the big-box stores every 40 miles down the road with mass amounts of firearms on display. Small town folks had little chance to compare models or even see something out of the ordinary. While every small town Hardware store stocked Remington 870s, Remington 742s and Winchester 94s, anything other than that had to be "special" ordered and not seen until it came in. Gun shows, even if you weren't buying, were a great way to see what was out there other than in the gun rag ads. Now most folks can travel less than 30 minutes to a GM, Cabelas or BP and see more guns than they could at the local traveling gun show.
Additionally, in Wisconsin, the 48 hour waiting period for handgun transfers has almost killed handgun sales at gunshows, unless the seller is local anyway.