It's indeed common to say that you should not / do not need to oil plastics, which is partly true.
Except that here we are talking about B&G that falls into the latter category, but totally different from a usual plastic chip.
May I ask what B&G chips do you have?
From my experience with BG's, oil is mainly used to give some shine to the chip. As you can see on the picture above, the scratches disappear, the surface becomes smoother. The oil leaves a kind of micro-film on the surface, so it is necessary to wipe well with absorbent paper, this step is crucial if you do not want to leave marks and make the tokens sticky, which would be the opposite of the desired effect.
And, B&G's are not slippery (even oiled), unlike any other "plastic" manufacturer.