The $500 million is less than 1% of their cost of goods. It's an easy place to look for improvements, but it isn't really a threat to their business.
I definitely think things have gotten worse. I've directly noticed a couple of thefts at my local Walmart in the last couple of years and hadn't seen any in previous years. In one case I saw a person just push their cart through a self checkout area. In the other, the self checkout I walked up to had an incomplete transaction sitting there.
The liability and reputational cost of a store security guard injuring a shoplifter, or even getting injured themselves is so high that they might not even be allowed to physically intervene. Naturally, knowledge of this spreads.