Do you know how much more money they would make if they would just do the most simple thing and check users ages?
Do you know how much more adult oriented games Steam would be able to feature and that way would be able to be sell?
Do you have ANY idea how much profit Steam would make over how much money they would have to invest?
I am sorry for being so hostile on this however I have seen this point over and over again and it falls apart every time someone puts even an ounce of logic to it.
Steam COULD do this. But just like with TF2, Valve wont pull the trigger unless they have to. They are lying in a made bed. Steam is printing them money. Age verification is something it doesnt require and therefor it wont do it. Money is not the problem, they make around 100 times the amount this would cost monthly anyhow.