There have been dozens of attempts at 3rd and even 4th parties since the Whigs disappeared. Even when the US had several parties they all fell to one side or another. Why didn't they succeed? Paul, Perot, Nader? They all had big followings but no one would vote for them. Various reasons not to do so as well. 3rd and 4th parties can happen at any time. Getting people to vote for them is a different story. Trying to say that there is some conspiracy to not let a 3rd party in is asinine.
We had a bigshot 3rd party big talker here in Texas this last election running for governor. He got lots of airtime and had a big grass roots push. He was beat out by the liberal guy who's name I've already forgotten. No conspiracy. He just couldn't convince anyone that he was the right choice (thank the baby jesus

).
Maybe if a 3rd and 4th party candidate would happen if they weren't as bat-**** nuts as the previous guys have been.