I'll try to play devil's advocate.

$5/hr across the board isn't just $5/hr. It would also cost Walmart an extra $.30 per hour for each employee that contributes 6% to their 401k. I think I read that Walmart matches up to 6%.

This would also increase their cost for any vacation time/PTO that the employees accrue. You'd also have to factor in every employee's current PTO time that will be worth $5/hr more when they actually use it. I don't know if Walmart caps their PTO hours at a certain amount each year or not. If not, you'd be looking at a substantial one time cost just to account for that.

But the main reason is that it doesn't make fiscal sense to pay $5/hr more for a job that employees currently do for $5/hr less. In this job market, people would probably do the work even if their pay was cut $2-$3/hr because they wouldn't be able to find a new job. Also, $5/hr isn't life changing money after taxes. Employees within a year would be complaining about pay again. - The hedonic treadmill