Where are all the L4D games hiding?

If I launch Left 4 Dead, click Versus -> Play Online, it says "There are currently 2439 people playing Left 4 Dead". Wow, that's a lot of L4D.

Then I see the number of open games, and it's less than 10, often just 2.

Why the big difference? Where are all those games happening?

It could be that this number is global players (?), and you might not be able to see games in your region. Alternatively, most of the people are possibly in full games, and so don't show up on the list. More alternatively, it could be that this number are currently in L4D, some of which aren't in a game, and others which are in different game modes.

Also consider that you have some filters that are screening the games out? Or perhaps region or otherwise. If none showed up I would say firewall...but.

If I'm not wrong, Steam will show you servers near your location (i.e. low ping times). I think the "Download region" setting in Steam's Preferences/Settings might also affect what servers you see, so make sure that's set to what you want.