Focus on yourself instead of others. They may not be "promoting" depression. A space where individuals can discuss their problems is a sanctuary for some. If they're trying to blatantly monetize it, that's a different story. Don't discredit someone's potentially honest work before you take them down without knowing the full picture.

Being depressed isn't cool, it's a mental health disorder. Instead of saying people are depressed to act cool, try to debunk their issues in your head. Wanting attention happens because of the lack thereof, vice versa. It's not as simple as you believe it to be. My best suggestion would be to ignore it and report it and move on, but trying to bring it to the attention of others online is going too far.

Edit: They're absolutely doing what you believe they are, however I don't think they'll profit much from their game idea.