What determines if a game has Steam trading cards???

I’ve had this question for awhile, but cant seem to find an answer. What determines if a game has trading cards? Is it just developer discretion, or determined by Valve? I was thinking it had to do with game size/player base, but I’ve seen small/unknown games that have them, and relatively popular games that don’t.

Also, is it determined pre-launch on steam if there will be cards, or can a developer add them as an update later in the game’s life? Thanks.

P.S. I was playing Evolution, the one based off of the board game (that has cards as gameplay), when I wondered what the steam cards were, and saw there weren’t any.