Earlier quoted context omitted.
Those are far easier to handle than, for example, changing a timing belt on a gasoline engine. Faster too... You need less qualified people, less time, less parts, less often for repairs that a handy person can often do themselves and save on labor and parts. Significant sources of income are therefore shrunk for dealerships.
Sure, you can replace brake pads yourself. But few people want to do it; let alone are capable. Saying "significant sources of income are therefore shrunk" significantly overstates just how many people would do their maintenance work on that level. I know people who have paid people to replace the bulbs on a car. My wife rarely even bothers to refill the washer and I can count on 1 hand the number of times she's chec…
To be fair most newer cars need a fair amount of front bodywork pulled to change a bulb and most crossovers require pulling tail light housings which can be kind of intimidating for someone who's never done anything more than changed windshield wipers.