I would say people generally underestimate how difficult it is to be a skilled bike mechanic that fixes things so they don't come back. When most of us fix our own bikes, it's a bit of an iterative process and we don't judge ourselves too harshly if we don't get it right the first time. Not to mention the people that screw things up and finally have to get the bike shop to clean up their mess at great expense. Working at the shop has shown me how often this happens. It's not every day, but a couple of times a month someone took a small issue and made it into a big issue.
The wait, especially right now, is a totally different matter. If you only rely on a bike shop for maintenance then n+1 is an imperative.