Agree. Some car places I use will allow me to bring my own oil (I prefer to stick to specific high-end brands) and simply charge "corkage" but if I was a car or bike dealer, unless I knew the customer extremely well, I'd only use the stuff I'd sourced, simply for the reputational protection and to save arguments.If you go to the dealer for oil change then you should use there bmw oil and filter,
if your doing your own oil change then use whatever you desire.
To me it’s almost like going to a restaurant and bringing your own food for them to cook.!
I side with the dealer with this policy since they are the factory representative and can’t or just won’t put in whatever you bring in a jug and then warranty there work. Not to say there isn’t better oil out there at better prices however that should be a DIY service.