When I was a retail manager at a big chain (not Walmart) it was made very clear to me that our job was to deter theft (with attentive customer service and proper use of control devices) NOT apprehend shoplifters. The safety of our employees was not less valuable than stopping a shirt from being stolen and our employees were not trained guards.
Dealing with LP issues was frightening. We have people come in with guns (store in an affluent mall). We had people break into the backroom while employees were there. We had mob-related thefts. The last thing I was ever, ever going to do was risk anyone getting hurt on my watch. That goes for employees, shoppers-- anyone in the store. I didn't want things stolen and neither did the company, but safety was always the #1 concern.
Also, if you stop someone who you think this stealing and you're wrong, it can open the company to significant liability (the brand I worked for lost a h-u-g-e lawsuit famously in the early 90s over a man who was accused of going into the fitting room and stealing pants when actually he had bought them earlier and worn them into the store, he wasn't stealing at all).
There are more reasons not to try to intervene in theft than there are reasons to intervene . We did always report theft to the police when an issue happened, and to mall security, and the corporate. But we never, ever tried to stop someone leaving with merchandise if they resisted.
This was about 20 years ago, but a large walmart type store near where I grew up ended up with a large lawsuit because their security personnel "detained" a man they suspected had stolen batteries and their detainment practices led to the man's permenant paralyzation. It turns out that the stolen batteries were actually dead batteries that the man had brought with him to be sure he bought the correct kind. It's really not worth hurting someone or being hurt over a couple dollars' worth of stuff.
I used to be management at a Target and omg there are some CRAZY loss prevention videos out there. When I first started working there, they were just starting to follow the "no touch" rule because all the things that had happened in the past couple years (employees getting stabbed, beaten up, lawsuits, etc)
I remember one of the videos they showed us was actually from a check fraud ring bust (I think) where an undercover cop was on the premises, waiting for them to leave the store. As the crooks are trying to make their get away, the cop steps in front of the car and OPENS FIRE (this is like mid afternoon time in the Target parking lot) on these people. Of course, the car guns it, hits the cop and sends him flying. Amazingly, the cop was fine but it was crazy to see on video!
I also remember watching one where a very um...large woman was basically shoving all these electronics into her fat folds under her clothes. They said she ended up getting away with around $2K in merchandise.