You may sue the criminal that stole your wallet for any loss you have. Walmart is not liable at all. I know you want to sue them since they have money, and the theft does not.
If you have fear of shopping , please get counseling, since having someone still a wallet is common place, you have a high chance of being robbed with someone with a weapon at a walmart parking lot, or a down town store also.
Unless you can prove, that the store knew this person had a history of this and did nothing.
Next if the police did not want to do anything, that is a police issue, not a walmart issue, to be honest, in many larger cities, you would be lucky if the police even came out
If you push, walmart may replace the money in your wallet, not because they have to, but because they are normally good at being helpful