Humans are a prosocial species. Cognitive and behavioral adaptations with social benefits, such as empathy, are strongly selected for. The ability to positively regulate the mood of others and the ability to have your mood positively regulated by others is a powerful one for a social species. Dopamine buttons like smiling and touching are powerful tools for a prosocial species. A brain that releases a massive amount of dopamine in response to music is exactly that ability.

The ability to understand music evolved due to the pressures that selected for speech and language. Blissful enjoyment of music is itself a social ability that was selected for by the same pressures that favored enjoyment of touch and laughter.