Because I’ve done it. Usually the ones stealing the stuff aren’t even the ones selling it. But, when you don’t have money and the only way to get your fix is to steal a list of stuff, you’ll do it.
No sane person wakes up and says “I have everything I need, and I feel safe and comfortable. So, time to go risk my freedom and future to start the day!” It just doesn’t happen.
Sure you have those outliers. You know, the house wife with plenty, but she steals for a thrill, but those aren’t the people stealing to sell either.