I'd love to claim it was overworked because we had perpetuated some great scam, making ourselves rich, and we needed to hide the evidence.
The rather more prosaic truth is that we just shred everything in the office to save working out what's confidential... The shredder is also closer than the recycling bin.
One day soon, one of us will crack and empty the shredder into the recycling bin. Until then, it will just keep overflowing...