Why do third parties run presidential candidates? Here are three big reasons...
(1) Third parties are forced run candidates for pres. because of election rules in some states. (more)
@WashingtonPost @PaulWaldman1 @GreenPartyUS @HowieHawkins @AngelaNWalker https://www.washingtonpost.com/opinions/2020/09/15/why-third-parties-should-stop-running-candidates-president/

Some states require presidential candidates for a party to achieve ballot status, which is necessary to compete effectively with major-party candidates in state & local races. (more)

(2) National campaigns are necessary to promote big 3rd-party ideas & solutions that the major parties won't touch. E.g. The #GreenNewDeal, introduced by Howie Hawkins in his 2010 Green run for NY gov., then promoted nationally by Green pres. nominee @DrJillStein in 2012. (more)

Progressive Dems embraced the Green New Deal (and watered it down) later.
(3) Pres. candidates help state parties achieve ballot status; help promote state & local candidates; raise money for them. Many voters don't take a new party seriously until it has a pres. ticket. (more)

Furthermore...
►It's not a two-party system. It's a #TwoPartyRacket. Dem & Repub legislators have rigged the ballot-access rules in many states to favor their own candidates and hinder third parties & independents. (more)

►First-past-the-post and winner-take-all elections are inherently anti-democratic. They should be replaced by #RankedChoiceVoting and #ProportionalRepresentation. Greens have been demanding these & other election reforms for years. See http://fairvote.org  (more)

►Let's not kid ourselves. @TheDemocrats want to destroy the Green Party, whose very existence reveals how deeply the Dem establishment has abandoned working Americans. Hence the spoiler label, post-2016 #Russia smears, and GOP-style voter suppression in Wisconsin this week.