Why did Martha's Vineyard homes increase from $700K to $1M in 2021?

NIMBYism restricts development (supply), so that the only thing that can adjust to an increase in demand (induced by the pandemic) is the price. From a 2021 NY Times letter to the editor: 

In the end, what really reads in this strange piece is that this gentleman didn’t like the Water Street apartments in Vineyard Haven for some reason, and is nervous about the Lambert’s Cove development. To this, there is of course an argument to be expressed and heard. But when it takes the form of such cynical bloat, it becomes a mockery of its own argument. It makes clear that the spirit of “not in my backyard” is as much of an obstacle to continuing to preserve the Island’s community as some self-interested folks, such as those who are pretending to oppose the housing bank out of supposed “environmental” issues. 

 ... I am also absolutely and constantly baffled when people complain about the one, sole affordable housing developer on the Island, a developer which takes great pains to protect the environment and build in accordance with what natural environment and cultural environment exists there, such as preserving and occasionally building around trees and trying to tear down as little as possible — and then conveniently miss the fact that every other building in Edgartown, for instance, has been torn down and turned into a McMansion over the past three years. If this attitude doesn’t come from self-interested hypocrisy, it comes from an extreme level of blindness.