It looks like you're new here. If you want to get involved, click one of these buttons!
So the famous digital games vendor Steam came out with a "Greenlight" program where a game could publicly request to be allowed onto the Steam store (which feels quite arrogant on Steam's part but that's not my point here), giving fans a webpage where they could upvote the game.
What started happening was that some games, in order to get enough support to be thus "greenlit" through this program, started being sold by other vendors who would promise Steam game activation keys (which are generally considered very desirable) to those people who bought the game early, such as in a bundle package like a Groupees, Indie Royale, or Bundle-in-a-Box bundle. (There are possible unauthorized distribution issues with this, and there are also possible solutions to this, but again, this isn't my point.)
Giving out Steam keys happens after a game is actually released on the Steam store. The game's publisher (or developer, self-publishing) goes through a process of requesting some number of keys from Valve (the company operating Steam), which I've heard doesn't cost the publisher anything. Then they distribute these keys to the customers, such as getting them posted on customers' purchase pages on Groupees, or in their Desura accounts. This process takes some time.
Unfortunately, some people really want their Steam keys. QUICK. In fact, there are some people who are even less polite about it.
What makes this worse is that there are indeed some games that haven't given away Steam keys after promising to do so -- this includes at least one game that went f2p and encountered somewhat of a marketing disaster in the process, as well as another game that went in a Greenlight-oriented bundle where Steam keys were explicitly promised and then declined giving keys out afterwards.
Ironically, though, I actually think that these people are right to ask for keys -- they're just going about it the wrong way, in my opinion. Because this game got released on Steam with a somewhat confusing process (it fell off Greenlight for some reason and then got released), but it was indeed sold in a bundle promising Steam keys to buyers.