> Why does something that is considered to not have any adverse effects labeled differently other than to confuse the consumer?

One good reason might be if there were an unfounded stigma attached to one of the names. Rapeseed has many common names in the English language[0]; what are they trying to hide?! (In large measure, the unfortunate connotation of rapey-ness.)

[0] https://en.wikipedia.org/wiki/Rapeseed#Common_names