This makes me wonder to what extent American culture plays a role in this survey, as American Buddhists tend to be fairly socially and politically liberal.
I think the more interesting question is why or how it came to be that so many American Buddhists lean to the political left. Especially American ‘convert’ Buddhists.
I suspect that a certain amount of it is a matter of self selection. How much western convert Buddhism tends to select for persons with certain political ideologies. How much of it is due to political minorities not feeling welcome.
Depending on the sangha, how long it takes for a new member to find out that unless you ascribe to a certain political orthodoxy you are not going to have a good time.
I know of a teacher in a lineage who put the question of what the group would and should do if a member said they voted for Donald Trump. That was a skillful and compassionate question in my mind. But I was shocked to find that this teacher was a outlier compared to other teachers in the lineage.