Liability They probably don’t train use of physical force. Most security is some guy who can’t qualify to be a cop and they give him a radio or cell phone.
My daughter was 100 pounds soaking wet and a smart gal. Mervyns hired her with a masters degree to be chief of security at their store. She use her brains and backed up her calls by showing up in court the cops liked her and gave her a radio system which went straight to the patrol cars.
But she was totally vulnerable if she and her employees tried to actually stop someone. No training, no experience. Follow them to the parking lot and hope the cops come out and hope they don’t pull a gun and shoot you.
So they had employees try to physically stop people when they had no training.
Knowing what i know now about store security. you can steal something in your clothes and walk out to the car. If there are no cops, you will get away.
Correction: These billion dollar companies don't "pay" to train their security people in the use of force. It's all about money/liability. They don't give a rip about sending some person out there to play security who has near zero training and are totally unarmed. If they only want an observer, just install cameras in the store and parking lot if they don't have them already.