Ah I see, you’re not American so you literally don’t know.
General elections for us are binary. We vote for Democrats or Republicans or we throw away our vote. There’s no 3rd party.
Primary elections are where we determine the candidates that will be put forward for each party. This goes for President but also every other executive branch office, at the federal and state levels.
Internal party elections are where we decide the party reps who decide funding, advertisement, official party endorsements, etc.
Bernie lost the primary election because his core supporters have no idea any of these other races exist. They show up, barely, every 4 years to vote for president.
More centrist progressives like me show up every single election. We are constantly pushing our agenda up the chain.
Flighty Leftist voters don’t stand a chance until they consistently show up to push their agenda.