The same thing happened also in Europe which didn't have that type of suburbia, nor necessarily that sort of WW2 win. These social changes were a slow ramp, not some single event changing things. It was in part technology, in part state centralization capacity via administration development, in part ideologies and philosophies etc. Both socialism and capitalism pushed against traditional kin and clan structures in favor of universal platforms (markets, or universal co-ownership). But already the Church laid some of the foundations of all this. And then the church also weakened as a slow erosion and social norms were markedly more liberal in e.g. the 19th century than in the 18th and so on.