Why are we working 3 jobs and still can't make ends meet?

This has been on my mind for the last few days, I just don't get it. I have 3 jobs and so do a lot of other people I know, but I still struggle to pay my bills and put gas in my car. Why is this? I work a lot of hours but it doesn't feel like it adds up to what I need. I make a pretty good wage, but the prices of things just keep going up and up.