Why do we buy junk?

Because the status games we're forced to play. In a fiat economy, the status games are all funded by debt. So-and-so got a new phone, now I do, too. So-and-so got a new car, now I have to as well. So-and-so got a new house, sent their kid to a particular college. All the status games are fueled by bringing consumption forward.

Status games are by nature zero-sum and very high time preference. Yet people play them because they're social animals.