Have You Played... Steam Trading Cards?

Have You Played? is an endless stream of game recommendations. One a day, every day of the year, perhaps for all time.

And if so, do you still? And if so: why?

I've tried to understand the allure of Steam Trading Cards before, and despite briefly being entranced by this most intangible of Skinner boxes, I was left perplexed as to why so many people are so caught up in this game of pretend swapsies. Untold thousands are: if I put a card up for sale at the current going rate, it's usually sold before the day's out. People are buying these things feverishly, desperate to complete sets and...

...And then what? Is it an expression of fandom for particular games? Is it just to scratch some completist itch, a dissatisfaction that a number in the Steam interface is not as high as it can be? Or is it simply earnest pursuit of a freebie or discount code? Or is it something I've missed entirely?

I did trading cards as a kid. As a teen I even got pulled over by airport security because I had a big box of X-Men cards I was carrying around everywhere just in case I stumbled across a comics shop which might have booster packs, and the big block of foil shinies inside it triggered the scanners. But these were tangible things. I'd fan them all out on the floor and admire them, feel like I was building something. The Steam cards interface doesn't even simulate something like that. Where's the joy in it? Can it really just be compulsion and bargain-hunting, or does this all go so much deeper?