Why is On-Site shredding more expensive than Off-Site?

Historically, Off-Site shredding services are companies in the recycling business, which have added a dimension to their business by offering shredding. They are able to sort their clients documents into the various types before shredding and get a higher price from the paper mills. They are also able to save money by using a much less expensive truck for collections than a truck configured with a shredder.