Desktop computer? They probably decided it was either too big to carry away without being caught, or that it wasn't something easy for them to sell. I would guess that cameras, cell phones, and tablets are easier to sell. They're all one piece, don't look very different "used" or "new", and you could probably re-package them with some bubble wrap and an envelope. A desktop computer with lots of parts, some of them obviously used, is going to be a lot more obvious and harder for the thief to deal with.