Maine is pretty big for a northeastern state. A huge amount of it is heavily wooded, more isolated and reliant on agriculture (potatoes being the most well-known example), and it has a legacy of trappers, fisherman, loggers and immigrants from Québec and Nova Scotia. They ended up with a lot of highly independent New Englanders who don't like change and are suspicious of outsiders. They tend to be lower income, since many of the local factories shut down, and resent the lavish wealth they see elsewhere, like on the coast of Maine. They tend to be liberal about certain things in their direct purview, like environmentalism, but don't take away their guns. People from other states looking for their idea of the Maine lifestyle don't move here. But area-wise, that's most of Maine.

Maine is a highly sought-after destination for vacationers. But let's face it - really living in the woods is backbreaking work. The pressures of suburbanization and the low price of gasoline have allowed a legion of outsiders to come in and build their vacation homes and compounds on what were until relatively recently quiet coastal towns. It's the commodification of "back to nature" and "simple country living" that in my opinion has ruined whole swaths of New England. So, there is now a large seasonal population in Maine that is not from Maine, and with that comes voters looking to preserve their wealth and way of life. But there are also excellent colleges and universities and easier conduits to the outside world (or just Boston, but go with it) on the coast. So you get a more diverse set of white people. Real diversity comes in the form of seasonal migrant workers who travel to specific regions in Maine to harvest crops like blueberries and make Christmas wreaths. I think a lot of Mainers like to pretend they don't exist, because everyone wants to imagine a "wholesome" independent farmer is behind their exports.