Mechanics are expensive, but buying enough equipment to do any kind of major job is even moreso. Not to mention the cost of trying to do complicated jobs without technical expertise, which could cost you a lot if you make a mistake.
Im all for doing work myself when its within reason and doesnt require much in the way of specialized tools. But theres more than a few reasons that mechanics cost a lot of money. Expertise is expensive, labor is expensive, equipment is expensive, etc. Some things are best left to professionals. Unfortunately we are long past the time of cars that are truly simple for the average person to maintain or learn to do work on