"I do not understand renting a table for display only"
I truly understand your point.
However,, many collectors do enjoy just doing displays. Sadly,, there aren't enough people that are willing to do just displays to where it can be affordable to put out just a "display show."
A lot of gun shows do rent tables to displayers that do nothing but show stuff. Heck, the NRA Convention/Show coming up has a lot of that. Plus,, vendors & manufacturers will be there showing stuff. No gun sales,, but other items may be offered.
But regular gun shows,, often have various collectors groups that DO get together & put up displays of their stuff. Ruger Owners & Collectors Society, (ROCS) do shows across the country, and it helps promote Ruger interest, collecting & also EDUCATES a lot of people about Rugers. The same goes for other firearm collectors groups. Thanks to going to gun shows,, and seeing "just displays," I have enjoyed admiring rare, unusual, famous, one-of-a-kinds, and all sorts of things that were just displays.
In fact,, my own experience in it,, LONG LONG ago,, (about 1980) I went going to a gun show where Bill Hamm had a display. It allowed me to realize there were Ruger collectors & all kinds of interesting things ABOUT Rugers. It educated me and I decided to dedicate a lot of my enjoyment of Rugers into a life long event. I've been doing displays,, paying money for tables, the expense of motels, meals, gas & my time,, JUST to display.
And by doing so,, many collectors are able to meet folks who may have something to sell, and we've been able to add to our collections.
But the biggest reward is helping another person with something about THEIR Rugers. I have several good stories about meeting strangers who had a question, or needed something, or whatever,, that I've personally helped.
To me,, the time & expense of "just doing displays" when these things happen goes well beyond the money it cost me to do it.
Oh, and I've driven much more than 80 miles (one way,) to do it for every show I've displayed at. Living life is not always about money.