That is because, like real life, it isn't some sort of sci-fi model world where architecture is generally the same all throughout. It's all of the above - art deco, gothic, and brutalist. Spread out throughout different regions. They wouldn't look the same all over the US, obviously.
Boston felt strange in that it was essentially what a town in the 80s would look like, with a couple of minimalism combined with art deco to demonstrate the contrast of Fallout's science advancements with the world the advancements are being made in. I always thought that the vibrant, curved skyscrapers were constructed to demonstrate the possibilities of a complex construction material made by Vault-Tec or something. As sort of a demonstration of the material they use to build Vaults, or some form of similar advertising.
But it felt like they literally stuck the buildings like toothpicks straight into random districts to increase variety, rather than showing the dynamic sprawl of buildings like that. There were, in Fallout 4, always two of these buildings surrounded by whole blocks of brick and mortar structures, so that's why they felt out of place.