In Europe, I think war was a major motivation in moving towards simpler styles. The Bauhaus movement was adopted in some quarters after WW1, because some people wanted to leave behind the pre-war regime(s) which had led to the war. After WW2, there was a more practical demand, i.e. a need to build large quantities of housing quickly to replace stock destroyed by the war and rehome vast numbers of people. Certain modernist styles were seen as cheaper and faster to build. Khrushchevkas reflect that and destalinisation.