Everyone is touching on factors leading to the weakening of gun shows. I'm no expert here but in the few shows I've attended since moving to North Carolina, my observation is that the market is saturated with firearms and related equipment perhaps from over-production. There are thousands of used hunting guns available, more AR-15s then would be needed to re-start the Vietnam war.
New gun models appearing nearly daily with fewer places to use them.
Then, all businesses are subject to general economic, business and financial conditions. Gun shows would be no exception. The Coronavirus shutdown certainly didn't help. I'm willing to pay up to ten or 12 bucks, with free parking to walk into a gun show. At fifteen dollars or higher, the show is no longer worth it and I would walk. At my age, its time to part with toys, not add more.