He stood alone at Gjallerbru... and that is answer enough.
- The executioner has always been more or less a loser and bufoon 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, she 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 Skrurge. 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 undeads of Hel close to them. They arrived to the bridge to the exit, and Thor announced that he would stay, so that the others could escape. Skrurge attacked him from the back: HE will stay, he just need a pair of machine guns, and some ammo. And he did it: nobody could pursuit the Asgardians.