But many Steam users value the Trading Cards because a complete set within a game can be traded for a game-specific badge that will be tied to your Steam account and profile page.
And because of this market opportunity, a wide variety of software "bots" have been designed to mimic human activity in your Steam games, thus earning trading cards without the need to actually take time to play the games themselves.
There are some exceptions, though, like when some Argentinian gamers discovered that the vagaries of currency arbitrage meant they could actually make money by buying certain bargain-priced games and selling the resulting trading cards on the open market.
To prevent players from farming "free money" from trading cards in free-to-play games, those titles usually don't drop cards unless you spend money on DLC or in-game items.In fact, in 2017, Valve had to take action against "fake" game developers who were abusing the ability to generate free Steam codes for their own games to farm money from the generated trading cards.
Valve can manually turn off trading card drops for free games when it sees this happening, but often the damage has already been done by the time the company can react.