Walgreens has already had to admit they have lost revenue with this practice. Perhaps an increase in shrinkage is overridden by the loss is sales? (penny-wise, pound-foolish, etc.)
I won't even shop in a store where I have to hunt down a salesperson to unlock the dressing room, let alone unlock a cage. There are also plenty of examples of discrimination in the types of products they decide to lock up vs. not, and it's NOT just price and size.
Either way, if you're going to treat me like a thief before I can even put something in my cart, you don't want my business. Almost all of these anti-theft measures could be counteracted with better staffing.