How does Steam benefit from giving out cases?

This might sound like a question not related to economics, but I've tried to imagine this situation in traditional markets and it does not make sense. I've gotten like 50 dollars this year just by playing CS2 a couple hours a week. I am getting cases, selling them and buying games. This implies, in my opinion, that steam gives the developers steams' money, and this is obviously bad for them. So how does it work, why do they do it? And can someone provide a similar example in some traditional market.
It feels like I'm so close to the right answer, but I just don't get it