The gutters are sloped aft to keep them from filling and getting the slf damp whilst parked and doors open. Also. If level, they confuse the rain runoff.
That's a given. But their angle of dangle is not arbitrary - it's calculated. Best seen on the A321 where the mid doors are at a lesser angle that the fore and aft doors.
And this is good gen from a mate who was on the Airbus design team.