hand-eye co-ordination has a timing element. that timing element is based off of emipirical sampling from the environment. music is also structured in time, but it pollutes the time-sampling process when you do something like parralel park with limited visibility.the brain doesn't have enough bandwidth to process incomplete information sets (parking) and embellished information sets (music) at the same time.

TLDR: music is distracting (in this context)