Four four common time replicates the heartbeat and natural bodily rhythms but that does not really explain why music can so successfully alter emotional state in the listener. I think it is not really known why other than music connects with and is readily understood by organic brains, not just human in a very intimate way. For example a five minute piece of classical music is informationally very complex but a person is often able to hum it back after a single hearing and do so again years later. Repeating verbatim a five minute speech listened to is beyond most people and so it might be suspected that music is more native to the brain than is language.