There are voters who hanker for a third party. I'll make three brief observations:
i) We already have a third party. Indeed, we have a plethora of third parties, viz. Green Party, Constitution Party, Libertarian Party, Objectivist Party, SPUSA, &c.
ii) A basic problem with the idea of a third party is that that's all it is: an idea. An abstract ideal of what some voters would like a party to be. A party purified of compromise. A party whose platform and candidates share their particular views. A voting block composed of all and only those who share the same outlook and objectives.
a) One difficulty is whether there enough like-minded voters to make that a viable, national party.
b) Another difficulty is that we lack the control over human behavior to make all like-minded voters join one ideologically pure party. We can't create that party by fiat. We can't decree how people will associate politically.
iii) Another basic problem is that third parties are apt to be most cohesive when they have the least power. When it's just theoretical. In that situation, it's easier for them to paper over ideological factions within their own party. The stakes are so low.
But if a third party suddenly had the prospect of wielding real political power, the faultlines would become active. Suddenly, they'd have a chance to…you know…do something. So then it would become a question of, Okay, what should we do with our newfound power?
Consider the libertarian party. By definition, libertarians are united by some things. However, on social issues, they range along a spectrum, with secular libertarians at one end and Christian conservatives at the other end. Some people (especially young men) are libertarians precisely because they want to be let alone. "Get off my back!"
If the libertarian party become a viable national party, divisions between the secular right and social conservatives would surface with a vengeance. Both sides might agree on freedom to opt out of the homosexual agenda. But on bioethics, there'd be a fundamental conflict in terms of what the state should permit or prohibit.
And that's just one example.