Why do loggers say they can not cut large live oak trees?

Loggers are in the business for profit.  It costs money to cut down trees that usually do not have any marketability.  Receiving mills usually do not like live oak as it is extremely hard on the equipment due to the wood density.  The trees may also be too big for use as most mills have a maximum diameter that they can purchase.  And, there may local ordinances that prohibit the harvesting of large trees, and in particular live oak trees.