Why don't employers give me a chance?

I don't understand why the whole job application process is so complicated. Why can't you just offer your help to someone who needs it and they say ok and let you work for them. I understand interviewing for a high responsibility job, but why for something simple like a stock worker. Why can't they just let me work for them? If I'm really that bad or "unqualified" they ca just fire me. I won't lose them thousands of dollars. Are human beings really that full of themselves?