I mean, if Bernie won in 2016 or 20, he would be a better president than Biden or even better than he is as a Senator right now, because he would owe his position (and reelection chances) to the left donor/activist base. And a bunch of liberals would probably support a 3rd party candidate against him, so even as an incumbent he would probably have big problems with getting reelected. Right now, he is a Senator, if he wants to run again in Vermont he can easily do that and he doesn't need the left base anymore, since he is not running for president ever again.

So instead he can support whatever policy positions he actually wants, OR he is trying to win favor with Biden in exchange for some small policy crumbs in some other area (something that he should know doesn't work with any liberal politicians, but again, I guess he is just old). In both cases, I disagree with him ideologically, but he is an old guy who is probably retiring from politics soon, so whatever. The left should not be too hung up on individuals, remember that politicians are just a tool to implement policy. The really sad thing is that it will be harder and harder for a Sanders-style candidate (someone who wouldn't actually owe his position to big corporations) to even run for the nomination ever again, especially since big money interests kind of figured out they "only" need to outspend left-wing candidates by around 3:1 and they've been very successful in recent elections.