He stood alone at Gjallerbru... and that is answer enough.
The Executioner has always been more or less a loser and buffoon as a villain, and never a serious threat. He was seeking the Enchantress, which he loves, and she turned him into a tree for interrupting her while she was seducing Heimdall. So, he joined Thor in his mission to Hel, to be away from her. Once in Hel, he found her again, because Heimdall has killed her, and deserted to stay with her. It was a trick of Hela: this "Enchantress" was actually someone else's spirit, pretending to be the Enchantress to manipulate Skurge. He got really angry, and instead of attacking his comrades as Hela was expecting, he destroyed Hela's ship. All the Asgardians escaped, with the undead of Hel close behind them. They arrived at a bridge, and Thor announced that he would stay, so that the others could escape. Skurge attacked him behind and insists he will stay, and hold off the forces of Hel with two M-16s. And when he runs out of ammunition, he uses them as clubs. And he holds the bridge.