If you’re thinking of a scenario where magically a majority of voters all vote for a third party
That's literally what they're implying. They're straight delusional. And, unfortunately, there's a LOT of voters and non-voters out there that are as well.
Have you considered that maybe part of the reason is that we keep slingshotting back to Republicans every other cycle and they do what they do best and fuck everything up, exactly like they're doing now?
It's massively disingenuous to imply Democrats don't do anything. They have a PROVEN track record for being better for our economy. They've regularly bolstered social support programs. They passed the ACA/Obamacare, which definitely helped me when I was younger. They've worked to forgive student loans. They don't make a hobby out of violating Constitutional rights. They don't send masked goons into our cities to kill Americans. They don't threaten our allies. They don't impose tariff taxes.
They aren't perfect, and clearly we should expect more out of them, but they definitely do get shit done and are a WAY, WAY, INFINITELY better option than Republicans and, realistically, the only other option on a federal level.