It was RL’s idea which was inspired by Nev. The goal is to make it so that Poe is still the morally righteous one of the trio which plays better off of the ex-stormtrooper and scavenger. It makes it more funny that Finn is poking at him for it because it probably genuinely annoys Poe that he had to do that stuff. Plus, it lines up better with canon than the retcon which TROS introduces. He could have done this mission for the Republic at any time while he was working for them. True, it’s stupid of him to go back, but desperate times and all that. He definitely did not want to get caught by Zorri, that’s for sure.