Why are we seeing a shift from plastic pallets to wood?

Here is an article that explains the decrease in plastic pallets and the increase in the difficult to handle wood pallets.
The Case of the Pilfered Pallets
"...The demand for plastic resin has driven the price of reground material to as high as 60 cents per pound. A trailer load can fetch as much as $10,000. "I was recently contacted by a postmaster in a small, rural town in Oklahoma," says Vogel. "He had found hundreds of our pallets in a company's yard, waiting to be shredded... His other piece of advice is to decline to buy or use a pallet if it's stamped Property of USPS." Unless you are an authorized user, you will be breaking a federal law. ..."
Reference: www.mhmonline.com -