Why do head phones always have only one side die?

I’m starting to think this is on purpose. All of my head phones, and I now have 8, all die on one side or it gets considerably weaker sound. It also doesn’t seem to matter how much I paid for it. Am I doing something wrong or is this just so we go out and buy another one? I remember when they could last years. Now I’m lucky if they last 2 months.