Having been in there shoes, I can relate.
Costs add up quickly and can be A LOT.

As an example Carlisle for me was a days drive each way. several tanks of fuel. each cost approx $100 . thats $300 each way in fuel alone.
Hotels gouging drives costs up, I got there Wednesday afternoon, Spent Saturday nite on the road headed back home. So figure $500 - $600 if your lucky
Spaces were $85 ea, I had 4.

Now, add in inventory costs . I figured I had to do $3000-3500 to just break even. For me getting ready for the shows started weeks in advance.
Once home from Carlisle I had to basically start all over a few days later to get ready for the Nats a month later

Now, toss in everyone wants a show special or wants to haggle. Or saying they can get it on ebay for cheaper, And there are ebay sellers selling for barely over costs ,,,just to sell.makes it tough on the ones trying to make a living at it
You can see these big shows ARE NOT CHEAP . Now multiply this factor by about 10 shows a year.
Costs are only one of the reasons ( but are a main one Im sure ) vendors have gone to online sales only or maybe just the bigger shows if at all ,

I enjoyed doing them as I liked the face to face interaction with customers. But after a while it took its toll and I decided to call it quits several years back