From my experience NIMBYs are typically local property owners who don't want their view, neighborhood, etc. to change. These folks could be better off financially than their YIMBY counterparts who maybe don't own all that same property.

If there's a group of people with money and a group with less debating the same issue, I would expect the politician to support the party most likely to make large campaign contributions.

I have no data to support this idea and should not be taken seriously in this context.