Kids picking up carts aren't going to detain anyone. It's the detaining that makes it work. The cops just come pick them up, they have eyewitnesses and video. Easy work.

The security guards that do the actual detaining are often off-duty LEO picking up extra hours. Even Kroger here has an armed officer at the exit door. So they can legally detain you and even arrest you.

True that they don't care about the bike outside. It's not their property.