As far as I understand it, stuttering is basically having faulty ”ram memory” for speech production. To produce speech you need to figure out what you want to say and simultaneously transmit that ”script” into a complex mechanical system of muscles and breathing. Knowing what to produce (the lyrics) and how to say it (the cadence/melody) will greatly offload the complex speech process, since that is a large part of the process being externalized to non-faulty sections