Because in this there is cooperation upon sin (ta’awun ‘ala al-ithm), that is, cooperation in sin, and this is forbidden because of the statement of Allah, the Exalted: “And do not cooperate in sin and transgression.” Especially regarding intoxicating drinks, ten people have been cursed who are involved in this business in one way or another, even if they are merely working as laborers.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 5715