I don't know if the DNC would even allow a candidate like Yang to ever become the frontrunner. They run boring, milquetoast neoliberals because that's precisely what most of the center-left want: a boring president that you don't have to worry about.
On the other hand, the imminent recession caused by COVID could be its best shot for years to come. The moratoriums for millions are about to end and food banks are getting longer lines every day. Something drastic needs to happen in order to avoid an even bigger disaster than it already is. It'll get shit on by some of the right for being "socialism" while the establishment continues to ignore every problem in the country in it while continuing to suck up to its donors, but I don't really see a better opportunity.
This is not true. Obama was a remarkably unknown state senator and came in at a time when he was given almost no shot. Hillary Clinton was a enormous favorite and Obama won people over with his message of hope and great change. Obama invigorated many people and ran 2 very successful campaigns. Regardless of what you think Obama did or didn't do for America you have to agree that he was by no means a "boring, milquetoast neoliberal" candidate because he was the complete opposite.
I'll admit Obama was a breath of fresh air. He is an exceptional orator and his everyman image certainly helped, but the outside figures certainly boosted him in 08. The recession was in full swing and opinions were turning sour towards the Iraq War, something both Clinton and McCain were adamant about continuing. Much like with Trump, voters were convinced that they could challenge the status-quo with the "outsider" candidate that was Obama. I think he really tried at the start but slowly got worn down as Republicans and even his own party simply couldn't get anything done without butting heads.
The thing is about his run is that he was a one-in-a-million candidate. The exception to a pattern that had remained unbroken since Humphrey. Just look at the previous Democratic candidates from the past 35 years: Kerry, Clinton (Bill), Gore, Dukakis. The common denominator here is that they all ran boring campaigns with meh levels of charisma. These people were definitely milquetoast but still got the nominations. That is the normal, and will likely remain so until you get someone similar to Obama, which I don't expect will happen for awhile.
You are right about 2012 Obama though, he ran a perfect ground campaign and Romney just couldn't turn out the more grassroot Republicans.
I think people are starting to realize that running an exciting campaign built on hope does not translate well into actual legislation. While he didn't get the nomination either of the two time he tried, Bernie would most certainly turned out the same way had he won, ran a campaign promising change only to be battered down by opposition from the GOP and more centrist Democrats. The outcome of this is ultimately cynicism. We can't expect people to put faith into a system that constantly lies to them and doesn't produce anything but gridlocks. Sooner or later that hopeful campaign shtick is going to run out of gas.