Also, apart from what other people have answered, Vermont has always had the reputation of being a pure and agricultural land that is unsullied by the nastiness of industry and the sins of cities. In the 1880s, there was an influx of wealthy industrialists wanting to make homes in a better area for their families. In a lot of ways, Vermont was seen as the pinnacle of wholesomeness.

So, you have barons of industry moving to Vermont, buying land and building mansions. They imported specialist labor like Italian stoneworkers for their specialties. There were architects such as Brattleboro Native Richard Morris Hunt that specialized in designing these estates for the very rich.

Also, it was very common at the time for rich people to fund projects for the public good such a libraries, churches, hospitals, schools etc. for various reasons from keeping a good name in the community to building a family legacy. Vermonter Lambert Packard designed a bunch of beautiful buildings during this time period - churches, office blocks, banks, schools and museums.