Crucial detail from the article:
The Burlington Democrat called it a “winnable race,” saying that polling showed him getting within 10 percentage points of Scott. But to prevail, he said, he would have to wage a “scorched earth” campaign with negative attack ads. He said that such a race would be bad for the state and not the Vermont way.
Despite the positive spin, this reads as if Dean's polling just wasn't solid enough to justify a roll of the dice on returning to electoral politics in his mid-seventies.
I am grateful to have been spared a really nasty campaign, but I also worry that this is a sign that Democrats will just give up on getting more serious about reigning in the state budget. Why bother when they can let Scott do the dirty work and throw a fit that he's not signing off on every new spending bill that the legislature passes? Dean's attraction wasn't just his name recognition, fundraising heft, and experience, it's that he's a fiscal moderate in an increasingly profligate party.