He did so not because a loud voice was necessary for resurrecting the dead. A whisper, or even His thought, would have sufficed. Rather, He did so for the benefit of the unbelievers witnessing this event. Regardless of how many corpses were in the vicinity of that tomb, none but Lazarus was to come forth. And this is true both in quickening the physically dead and the spiritually dead.
None deserves to be quickened.
But Jesus will quicken all His elect, those whom He loves as He loved Lazarus. Jesus' decretive command cannot be disobeyed. And he who had died came out bound hand and foot with graveclothes, and his face was wrapped with a cloth. Jesus commands the same for all whom He regenerates in conversion.