I don't expect Walmart to want to pay more out of the kindness of their hearts. Corporations exist to make money, not to be kind to people. That's where government comes in and why we have minimum wage laws, otherwise Walmart would pay $4 an hour if they could get away with it.
As for why people work for them? Come on man...Unemployment rates are high. Even though the average rate may be 7-8%, for the marginal and those in rural areas, it's probably 3 or 4 times that. NOBODY works at Walmart because they want to.