It's probably because you want "Half-Life News and Tutorials" on the banner, so sticking with HL pics would be the ideal option. L4D and TF2 are not HL.
True, but one minute everyone is telling me the site is not just HL and now it's the other way round. The only reason the name is Half-Life News & Tutorials is the fact it binds all games and mods on Source under one umbrella.
Time to wrap up, I'll collect the images & set up a poll later today. Remember that Blink, as the owner, operator and man in charge here at Interlopers has the final say in what's going up on the site.