What if they did? Even in the unlikely event that either candidate was denied 270 electoral votes, There has to be some tiebreaker. This is the system we have. Would it be better to make all third parties illegal?
We do have a way to deal with less than 270 EVs, each state gets one vote.
But no, Third Parties are VERY IMPORTANT for two reasons:
1. They can cause weak candidates to lose, decisively (as Bush Sr. did, and Biden may well do).
2. They can possibly win the top job, as Perot was close to doing, until he called it off.