Why would Bernie want to be Veep when he has more power as a senator?
It's the only way to control him. Bernie in my book is the kind of person who, if he lost the primary again, would make sure his supporters throw the election again. Vindictive and malicious little man. The BernieBros would also not accept Warren as VP. For them it's "Bernie or Bust." They represent a danger and dagger in the back to the Democratic Party. Unless he is on the ticket, any ticket will lose to Trump.
This. Bernie is evil and trying to destroy the democratic party, it's all his fault Clinton lost.