Simply because of extra taxes on brand names.
I didn't had to tell before until now, since 2004 i was importing replacement body parts e.g. hoods, door skins, fenders, boot lids & few other things among bumpers from Thailand for some specific Honda & Toyota dealers only. We call those parts "Teen & Plastic" in our term.
There are two types of parts available, OEM & ODM. The first price difference is there just because of that, OEM follows it's own specifications and ODM follows other companies specifications, same company producing same part but different specifications.
Now second price difference is because of different customs, import duties & taxes for one same part, if your part or it's box/packing holds a brand logo you will have to pay almost double custom duty & tax than the same part without the logo and in a simple packing.
Here, almost all 3s dealers have their hidden workshops for body work where they do most of the repairing specially for insurance companies or just by saying you that they are out of space in their 3s workshop & now they are moving your car to their second workshop, as you all know 3s dealers are bound to purchase all replacement parts from the parent company which are called genuine(ODM) and expensive than market parts called OEM.
Now here comes me(for example)! I import most replaced cheap logo-less body parts for them which they sell at company invoice price, at this point everyone is happy, client is happy, insurance company is happy, 3s dealer is happy & i am happy.
Please pardon me if it doesn't make any sense because i don't know what i'm talking about...?