The reason why Bai Mojiao followers were waiting outside was very simple, because this tomb was like the lifetime savings of a ruthless expert, not to mention he was supposedly the Devil commander, or might even be an unknown emperor level master. So, it was obvious that there would be layers after layers of traps to stop the intruders.
If they rushed inside, then the loss was inevitable, so it was better to wait until the other experts would rush out with the treasures. Their plan was indeed very good, but the unexpected happened, and not even the truth ninth stage followers were able to escape from the Swordqi attack that fell from above all of a sudden, and crucified them on the ground.
They never thought that their plan would backfire, and they would be the victims in the end!