Two reasons. There were some alleged cultist/idolatry practices involving wine that would cause it to become non kosher so it’s easier to just blanket ban anyt

Two reasons. There were some alleged cultist/idolatry practices involving wine that would cause it to become non kosher so it’s easier to just blanket ban anything handled by a goy. I think boiling makes it unusable for those same rituals. It’s also to discourage fraternising (especially romantically) with goyim.