Most of the reason is liability transfer.<p>Walmart can be sued for detaining someone wrongfully.  The police, not so much.<p>As for the solution: the police simply start showing up at Walmart much more slowly.  Once a Walmart gets a bad reputation, its business will slip away.<p>The fact that the police actually <i>hang out</i> at the Walmart tells me that they really don&#x27;t have something better they should be doing.