This is the security lock feature nearly all stores have now a days. It is to prevent shopping cart theft. They must go through the registers to unlock the locking mechanism. Other wise they will lock up. If you're taking the cart outside to look at outside merchandise; you'll need to leave it inside. 

Most kroger stores have had this security feature for years. There should be signs in the parking lot telling you about this. Chances are your blinders caused you not to see them upon entering.

The only annoying thing about this is protective parents that put their child in the basket and you have to tell them to pus it through the register not to the other side.