Answer: Because they want to advertise to the public that they have a $69.99 oil change. Yuk. Not sure about your BMW or whatever you may drive, but my BMW is not getting $69 worth of oil. I like it too much. How do they do that? Very simple.
The either don’t tell you what they are really using or they use a synthetic blend or conventional oil and make sure it is in very fine print. This is the amazing thing though, it is not the dealers fault really. The manufacturer tells them to do this. Let me give you an example. A 330i, 530i, and M3 will all get 0w20 or 0w30 at the dealership. They happen to use 100% non synthetic oil in their facilities which are still ‘approved’ by the manufacturer and meet all of their EPA standards because that is really all it is about and charge the customer a very low price. Problem? Yes. Your engine is getting the wrong oil and being changed at an excessively long interval.
At first we were all very excited to hear that intervals were being lowered but then they reduce the quality of oil they are using to a non-synthetic which cannot handle it whatsoever. We recommend you use a synthetic 5w40 in most cases and 0w40 would be another option. All of the engine oil we use and stock here is approved by the manufacturer but they don’t sell it because it costs money.
They are not in business to make sure your car lasts. They are in business to make sure your car lasts through the warranty period and do as little maintenance as possible during that time. Why they choose to destroy engines is beyond us besides them wanting you to purchase another vehicle.