Doing research, I came upon a list of oils & their shelf lives. I'm sorry, I don't know where it came from, but here are a few oils that are commonly used, & corn oil (at the end of the list) has a much shorter shelf life:
olive oil - 2 years
palm oil - approx 1 year
coconut oil - 1 year +
castor oil - 1 year
cocoa butter - 1 year
mango butter - 1 year
corn oil - 6 months - 1 year
That may be why it's not used often.