There is a saying in stock trading that goes 'you know nothing about a stock until you own some.' A similar idea exists in polling science -- you can get unreliable answers by asking people about something they have no vested interest in.

OTOH, people who put money at risk come up with very different rankings. The question is different so the answer is different. The question for gamblers is not 'who would you support/prefer?' but rather 'who do expect to win?'

Warren (pays) 7/4
Biden 10/3
Buttigieg 9/2
Sanders 6/1
Bloomberg 8/1
Hillary 14/1

Bettors believe that Hillary is about three times more likely to receive the DNC’s nod than Klobuchar (50/1), Gabbard (50/1) or Harris (40/1)

https://www.oddschecker.com/politics/us-politics/us-presidential-election-2020/democrat-candidate