Theybare because they are trained to be. You are actively dissuaded from any diag work, because it can be harder to justify your hours to the customer and dealerships are awful. For a mechanic, its a good and bad job. Nevermind ASE certification that encourages the same. Only small indie mechanics have the freedom to do good work.
Though I’m surprised “update” wasn’t a part of that official flowchart.
Have had dealership mechanics ignore my notes and identify a part as being failed despite my method of 100% excluding that part as being bad.