Main dealers are the only garages that can consistently provide poor service and still survive.
In fairness, they aren’t all rip off merchants. I use 2 different local main dealers for my daughters cars – Ford and Hyundai. Both provide first class personalised service and I’ve never felt ripped off. Both offer heavily discounted services for cars of 5 years old or more and these include free breakdown and recovery cover for 12 months as well as a discount on the MOT. They also collect and return the cars at no extra cost.
I suspect if I looked hard enough I might be able to get them looked after cheaper again at an independent, but the fact that we always sell the cars on with full main dealer service histories always gets us top prices when we change.