We used to do that, but thanks to a bunch of lame script kiddies, they ruined it for the rest of you. We had a small rash of people spamming our site in several ways. First, we had a few other people sign up and spammed our forums with a bunch of crap during a time none of the mods were up. The next logical step was to regulate who was registering. That stopped some of them for a bit. Then, we had people signing up over and over (a few hundred times actually), which flooded our mail boxes with "New user signup!". So, we installed the security text feature that requires you to type in the text embedded in an image to register on our forums.
Sorry for the inconvenience, but you can take it up with the a** wipes who like to ruin things for everyone else.