Why are so many retirees flocking to Maine anyway given its climate?
Mostly, we’re talking about Mainers aging in place. Like West Virginia, Maine has had a stagnant economy for a long time, so a lot of young people leave, but the elderly are left behind. In addition, the birth rate is persistently well below replacement, and the lagging economy combined with cold weather and lack of urban centers (even Portland is under 100k people) means very few immigrants, with many that did come being from refugee resettlement programs that have been cut off in recent years.
Coastal Maine is quite beautiful and definitely a regional summer vacation spot in the Northeast, so you do get some retirees from the Boston area and a smattering from the rest of the Northeast, but not many; it’s not a major retirement destination. There would be essentially zero retirees from Chicago or Buffalo, unlike someone else’s suggestion.