The original versions of the Walker trigger used in 721, 722 and 700 Remingtons had a safety which locked the bolt closed when on safe. The liability concern was that the rifle had to be taken off safe in order to open the bolt to unload. So, the locking arm was eliminated. For a while, receivers and bolts would still accept the locking safety. When the dust settled after the Walker trigger litigation, the new trigger mechanism was never intended to lock the bolt closed - the rifles could be unloaded with the safety on.
Three position safeties allowed the bolt to be locked with the safety on; bolt unlocked with the safety still applied; and unlocked and ready to fire.