i think it can be an additional revenue stream for the right detail shop.
my shop is retail only with very occasional dealer work. usually we are used by the dealers when their staff can't handle the workload. the relationship is normally temporary; as soon as the dealership hires new staff, our shop is forgotten.
dealers normally don't care too much about the 'how' of detailing. they focus on speed and price.
one former employee went to work at a dealership. they built a new facility. they did not ask for his input in setting up or designing the detail area. they have a garden hose and no specialized washing or detailing equipment at a BRAND NEW car dealership. this should give some insight into the 'dealership mentality' concerning car detailing.