Actually they tried experimenting with in-game ads at one point in CS 1.6.
https://www.bit-tech.net/news/gaming/ads_turned_on_in_cs_1.6/1/
Personally, I'm kinda amazed everyone forgot about ads in the MOTD that a lot of multiplayer source games had. Granted, the ads were set by the server host, not Valve, but yeah.
Tf2 community servers still have motd ads sometimes.
Actually they tried experimenting with in-game ads at one point in CS 1.6.
https://www.bit-tech.net/news/gaming/ads_turned_on_in_cs_1.6/1/
Personally, I'm kinda amazed everyone forgot about ads in the MOTD that a lot of multiplayer source games had. Granted, the ads were set by the server host, not Valve, but yeah.
Tf2 community servers still have motd ads sometimes.