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.
An official Peugeot mechanic told him that it would cost something like 4200€ to replace the unit, so he asked me if I could have a look.
After a quick search, I found an update for his system, burn it on a CD, and put the CD into its car.
The system updated, and then would work normally. Problem fixed for one hour of my time and a CD.