Why is the USPS delivery system so convoluted?

Date Time Location Event Details
August 12, 2012—- Greensboro NC US Departure Scan
August 11, 2012 11:25:00 AM Greensboro NC US Departure Scan
August 10, 2012 02:20:00 PM Capitol Heights MD US Departure Scan
August 10, 2012—- Capitol Heights MD US Departure Scan
August 8, 2012—- Bell Gardens CA US Departure Scan
August 7, 2012 08:30:00 AM Bell Gardens CA US Departure Scan
August 6, 2012 10:16:00 AM Paso Robles CA US Shipment received by carrier
August 5, 2012—- US Shipment has left seller facility and is in transit

This is from a recent purchase from Amazon. I live in San Diego. So if the item started out in California, why wouldn’t it stay in California instead of going all the way out to Maryland and North Carolina? What in the world is the positive logic behind this?