You can also check twitter for toyhou.se codes (it looks like people use the #toyhouse tag -- there are a few places that give out codes regularly too) or tumblr!
It's frustrating, but it has a lot of purposes: limiting traffic is usually done when their server can't handle a load (e.g. if they get too many people joining at once and they aren't ready for it, everything would get really slow, crash, and maybe cause other issues).
They're also still in beta (for how long? no one knows. maybe forever |||orz), so limiting traffic lets them add new features without worrying about too many people being affected if something goes wrong. It also helps prevent bot accounts from being created and spamming things up. Aaaand... it's probably a way for them to get money to sustain their servers (and probably grow them in preparation for more people? Maybe.)
(I hope that didn't come off sounding rude -- that's not my intention at all! I just think it's an interesting topic to talk about!)