Germany has always had a shortage of crude organic oil, and the US had a dramatic shortage during WWII. Both nations have developed advanced chemical industries as a result. Before WWII the major component of tire rubber was a natural latex sap from a rubber tree. The number of latex groves suddenly needed then would take years to mature if the military tripled them, so inventing synthetic rubber was a national priority.
The polymer (plastics) and elastomer (rubber) industries can be supported by chemically changing any naturally occurring oil. But the more you have to do to the oil to change it, the more expensive it is. Rudolph Diesel showed his giant one-cyl factory engine at the 1900 worlds fair burning peanut oil. You can imagine the difficulty in obtaining a tanker load of peanut oil compared to the simple distillation of crude oil pumped out of a well.
Corn oil can be used (to make any plastic or rubber type), and the left-over carbohydrate mash then fed to livestock, but orange peels have been a waste product for some time. Citrus products are a basic commodity in society because of scurvy. This leaves a huge volume of citrus peelings that are very cheap. Certainly some are ground up and mixed into animal feed, but extracting the oil is a smart move...