Car buying has moved almost entirely online before anyone sets foot on a forecourt - buyers research models, compare dealers and check reviews long before they visit. The dealerships that show up for “[brand] dealer [town]”, “used [model] for sale” and “car service near me” get the enquiries; everyone else pays AutoTrader for the privilege of a listing next to their competitors.
The reason why automotive SEO is worth the investment is simple economics: a single used-car sale carries hundreds or thousands of pounds in margin, servicing customers come back for years, and the searches that produce them repeat every single day in your catchment. Car dealership SEO isn't about beating the marketplaces at their own game - it's about owning the local and brand searches they can't serve, and turning your own website back into a sales channel instead of a brochure.