From WRSTC standards for OW diver:
"Open water certification qualifies a certified diver to procure air, equipment, and other services and engage in recreational open water diving without supervision. It is the intent of this standard that certified open water divers shall have received training in the fundamentals of
recreational diving from an instructor (see definition). A certified open water diver is qualified to apply the knowledge and skills outlined in this standard to plan, conduct, and log open-water, no-required decompression dives when properly equipped, and accompanied by another certified diver. "
The standards give limits to training depth but not to a certified diver. The training is for NDL buddy diving, NDL diving can be done to 190' although the agreed recreational limit has been 130' for many decades.
I believe the 60' limit is used to give a new diver a limit so that larger, longer, discussion of the whys and how's of extending ones limits can be skipped. Teaching good judgement takes time, and most OW training is about getting a diver trained quickly. The dive ops that require a diver to use the training limit is more about their clientele and insurance carrier than law.
Bob