Directly means being straight to the point and straight means going one way in the literal sense. But both can be used to imply that same thing like how "straight-forward" has the same meaning as "direct" .

They are synonyms. Directly - without anything in the way; without no one in between; without changing the direction or stopping;or without a delay Straight- moving in one direction without bending; a position that is leveled up, with no curves.