Why so many wood pallets?

 
Pallet Lessons from the USPS
"...Over the past year, leakage and budget concerns have led the USPS to re-evaluate its purchasing practices. The USPS has begun purchasing wood pallets, INCA presswood pallets and some low-priced plastic pallets. Peter Grau, a contractor to the USPS, said, “The action to purchase wood pallets over plastic pallets is due to budget constraints and asset management issues with plastic pallets. ..."
Reference: Pallet Lessons from the USPS