It would be helpful if you considered the points the others are trying to tell you.
1. Economics are governed by the laws of supply and demand.
2. There are a lot of stores out there selling stuff (supply).
3. There are potential customers out there looking for bargains (demand).
4. The margin between a store's profit and total cost is very, very slim.
5. Competition is keen and whole lines of advertising are used to directly compete for customers between different stores.
6. Walmart is competing with all those other stores. They have been very successful by having lots of great bargains. The customers are in the drivers seat, not the Waltons.
7. If they paid more in wages to unskilled workers, they would have to raise prices and risk losing customers which leads to going out of business due to keen competition.
These points are simple common sense built on knowledge about economics. I hope they help you.
Well done.