Why does wal-mart screw the good emplyees & promote the sucky ones?

I have known many employees that no longer work for wal-mart. I know for a fact that they do not like ppl that speak there mind & they expect the impossible from their department manager & send help the the teachers pets in stead of sending help to new dept. manager in training . Don't ask for help you will get written up & if you don't ask for help when taking on your responsibility you get coached .... either way you look at it they use & abuse EVERY employee & If they find one thing that they don't like about you as an individual you can forget making a career out of it . they will get rif of you in a heart beat..... I'm on the way out as we speak . Discrimination in wal-mart is running rampant! & it needs to be stopped.