Sorry to say they waste a lot of their earnings. There are better ways to creat personal worth.
Number one get out of debt as fast as possible. Then you have the financial breathing room to use your income to create your own wealth instead of making your lender wealthier. See?
They opt out of their 401k because they want the extra cash to have McDonalds or taco bell driven and delivered to their apartment via grubhub spending @25 for a burger they could have cooked themselves for $2. They drink only craft beer at $8 a glass as well. I think it's plain old economic ignorance.