Mass timer buildings are prefabricated structures made of (hopefully renewable) wood. The pieces are made in a factory and then able to be quickly constructed together on-site.
This can hopefully greatly reduce the amount of carbon in the atmosphere from producing a building. The cost of producing buildings in this method is also going down. Additionally, these mass timer buildings are typically more dense than single family homes, which can lead to more sustainable communities.
With blocks of flats I can kinda make sense of them existing, similar to how China has them for all the gated communities.
I’ll choose to wallow in anti-Americanism and assume that only they’re mad enough to have them for suburban collections of discrete, seperate, house style properties.