I'll apologize for sounding like a jerk in advance, but I don't know how else to say this: true understanding requires the ability to put yourself in their shoes. I cant speak for their specific situation but there's a few off the top of my head.
1. When doing mail order, they don't have to waste an hour listening to you or someone else complain or just shoot the **** on their dime. You wouldn't believe how many people go into stores just to kill time. The staff almost certainly have better things to do than sit there and politely listen to you or watch you wander around their store. People who go online or call have generally already made the decision to buy something.
2. Most people expect online/mail order to be less expensive. You complain it costs less, while others would complain if it did not. They can't win.
3. Theft is a huge problem. The reality is that everyone who walks in that store is either an opportunity for gain or loss. Can you guess 100% who is who? It's a real factor that raises the cost of doing retail business.
These are just a few potential reasons. So next time you get upset try to walk a mile in their shoes before you jump to the wrong conclusion.