Sometimes antigun groups put businesses up to this.
With tales of shootouts and mishaps in their store.
These misguided people think that if they post a sign, they are doing something, but as was pointed out, it keeps the people with the cleanest backgrounds, and those most law abiding out, who honor that sign.
If a business chooses to exclude CCW fine, but since a business invites the public on their property, and if anything happens on the property, fails to protect them, then we need to sue the hell out of them for creating a criminal nuisance of a place where people were denied a means of protection, and they failed to have armed security to protect them in it's place, leaving the public as sitting ducks.
These businesses need to know in addition to losing your business, that criminals are free to break all laws including their stupid sign, and will not be hampered from coming in. Sandy Hood, and Virginia tec were also "gun free" zones.