7 Answers

This would be the perfect question to ask of a Walmart manager.

There could be a number of incentives to be a productive employee:
1.  If Wal Mart is an "at will" employer, either one of you could terminate your employment, and there doesn't have to be a reason. 
2.  The better employee will be the one who will see his hours increased and opportunities for advancement present themselves.  Part time may offer no benefits, but once you earn a "full-time" slot, you may have medical, dental, retirement, sick/vacation time, and cash bonuses at various times through the year. 
3.  Step increases or classification upgrades.  At the end of 90 days' probation (or whatever they may have), you may get a small increase in pay.  There may be jobs opening up in the store (or nearby) that are "in house" only, meaning NOT open to the public. 
I'm sure there are many others, but those are some that may be valid. 

Here's one. Don't even "ax" about benefits!

Being shown the icy street in front of the store is enough of an incentive for most of the employees I know there. Psychological prompts are the main reason folks stay in such jobs. It is easier to work as an employee than to be your own boss in your own business with employees. Not being skilled as an employer is a sure path to bankruptcy. Family owned businesses often fail as a result inexperienced relations in charge of more responsibility than they can handle.

Fear!