Plenty of Republican city councils do this too. It's like the "personal freedom" switch is turned to "off" whenever you're in a city planning meeting.
My experience in my local homeowners' association has taught me that the only people who want to serve on the board are those who have an agenda and want to use their board power to implement it.
The three we had to put up with (until we voted them out) were all Democrats, as it happens, but your point is correct.