I dunno, it makes sense to me...
I mean, image somebody brings in their new Tesla for a loud mysterious rattle. Pretty much a brand new car, covered under warranty right? Tesla verifies the issue, tears the car apart and finds a LEGO into an air vent. Tesla doesn't want to be in a position, after the fact, of trying to convince the owner that it took 2 hours to get to their toddler's LEGO.
There are so many issues that appear to be warranty but end up being something else. It's my understanding that Tesla technicians are paid hourly no matter who is paying for the repair, I'm sure if at all possible they would rather it be warranty so they don't have to be calling us to get every little thing approved.