Ya I do not buy it. I know poeple say that, but its the same folks that want to fit 200 snakes in 4 ft of wall space.
The theory "Its less stressful than a large enclosure" Umm they are wild animals. Thats just a lie the snake breeders tell themselves IMO.
To say a bin does not mean small, you still need appropriate size. Yes many breeders keep them in too small a cage, but it doesn't matter what type of cage it is. The plastic bins are good for snakes because they help hold humidity. The standard tank with screen lid is often too dry. I have kept snakes for many years, and oddly some don't eat in larger spaces. I don't really get it either, but I have one like that now.
You are right, most breeders won't look like this. One per cage. The length of the animal should be less than half the perimeter. and we are assuming appropriate height if it is a species that climbs.
Don't be hard on snake breeders, there are good and bad. Keep in mind when I got my veilds the breeder talked me into two because they would be fine in a larger cage

.
But on the serious note of "Bad Breeders" If some one at a show seems to have more animal than they can handle. They probably do.
Many are much like puppy mills. I learned my lesson, assuming everybody at the show must be great herpers.
Ask questions, Are they excited about their animal or the sale?