No advocacy group against First Past The Post voting? Isn't the biggest concern with Jill stein running is that she is "going to steal votes from the democrats"? Attack the problem at its source, the FPTP voting system.
When we get to use a more representative voting system, people would be free to vote for Jill stein; secure in the knowledge that their vote would still be cast against the republicans if she didn't win.
Don't the democrats want to beat the Republicans in any way they can? Why is the DNC saying no to these extra votes? Don't democrats believe in democracy? Who could possibly say no to more democracy?
Almost entirely signal boosted as proof of a carrot that both will most likely never arrive, and most likely won't change anything even if it did arrive. There's a large difference between individuals pushing for something and them actually managing to get them passed at a scale that matters.