The problem is that it’s impossible to cook a well done steak that will hold up to the standards of just about any chef. We know that a well done steak will lose a lot of moisture and flavor. We only want to send food out that meets our standards, and that’s not really possible if the steak is being cooked well done.
Doesn’t matter to you, right? But we don’t know that. We know we’re sending out an inferior piece of meat, and our job is to impress the customer. What if they don’t like it, and then blame us?