Without support of candidates in local, state and mid term elections, these outliers really have no viable way of getting elected. They come out of the woodwork every four years to run a candidate for president and disappear for the four years in between. Then make a big deal about how they can never pull in a realistic percentage of the vote. In order to be viable, third parties have to be active and build a base organization starting at the local level, then state level. Once established, individual candidates can then move forward and receive more recognition from mainstream media. The closest we came to a third Party was the Tea Party, who worked very hard to establish themselves as viable candidates in local elections, then state, by pushing out old school Republican candidates. They worked on that base over close to a decade before getting their winning (barely) presidential candidate Trump into office. Any third Party candidate on the progressive side would need to do the same; start small and build up.
Right now, most third party candidates have zero political experience or reference and are viewed by the media as cute filler stories