if we're to guess, i would say that he didn't run third party b/c it was never his intention to actually.... you know, run for president.
the campaign was a fundraiser that got dangerously big, and once it became clear that if they weren't careful they might actually get somewhere, it was systematically f*d off.
controlled demolition, inside job, all the catch-phrases.
(what, no strategy to deal w/ the newsletter media backlash?)
(what, no attempts to organize support at the precinct level until waaaaaay too late?)
(what, lack of proper oversight of campaign employees from the bottom-up?)
(what, non-existent/ineffective campaign in iowa? new hampshire?)
...just a guess though, let the stone casting commence.