I think you guys have a very narrow worldview, thinking in terms of "us vs them" and "our team" and "Dem good R evil" etc.
That dichotomous divisiveness is not the game Bernie Sanders plays. He doesn't want to kowtow to the corrupt infrastructure of the artificial concepts of the GOP and The Democrats; he is thoroughly principled and has been for decades, and those principles got him that email list, and he doesn't want unprincipled partisan hacks like the DNC to exploit him.
You could say he "exploited" the Democratic Party by running as a Democrat, I suppose, but Bernie isn't stupid; he knows how to play hardball, he came incredibly close to winning the Presidency (NB: I'm not sure what delegate numbers you're looking at, but he didn't lose overwhelmingly - in fact he probably would have won, had one or two other candidates split Hillary's "conventional" voters (it's almost as if The Democrats including Biden had been instructed to step out of the way to ensure "YASS Queen" Hillary had a clean ordained path to the White House)), and now has earnt incredible leverage that can be used to further his principled policy platform.
You may think it won't work, and that Sanders is somehow going to be solely responsible for further losses in 2018 (hint: further losses are IMHO almost assured if the money-hungry tentacles of the DNC establishment continue to flail its slimy insidious influence), but after Hillary's absolutely incredible failures in 2008 and 2016 (and the failures of Obama to sustain support from 2010-2014), Cambridge Analytica or not, I think Sanders is justified in thinking that status quo political divisions are not going to help, and giving into establishment pressures is not a quid pro quo he gives a shit about for having run as a Democrat.