Major parties hate third party candidates for obvious reasons. Imagine if in football, it was legal for the camera man to occasionally run on the field and sack your quarterback — that’s what third parties feel like. It’s a disadvantage that comes out of nowhere and disproportionately affects one side. To make things even more annoying, in modern presidential politics, the only possible outcomes of a third party candidacy are: 1) Total irrelevance, and 2) Tipping the election to someone whom the candidate has denounced as the offspring of Josef Mengele and Satan.
Even so, I can see things from the third party’s perspective: How are they supposed build their party if they never run for anything? Building a sustainable party was Ralph Nader’s stated goal in 2000: If he had gotten five percent of the vote, then the Green Party would have qualified for electoral matching funds, and from there it would’ve been a short hop to full communism. Of course, Nader didn’t get five percent; he got less than three percent, including 97,000 votes in Florida, which Bush won by 537. But even though Nader ended up achieving the worst intent-to-result ratio since Catherine O’Leary went for a refreshing glass of milk and ended up burning down Chicago, his stated goal at least made some sense.