Well there is a strange logic that might explain it.
My personal experience is that mechanics ruin my cars. They always do something wrong. From over filling oil to incorrect coolant to damaging fuel lines, you name it, they've done it.
When they take this disgusting POS in, two things happen:
1) Nobody oversells them because they don't want to touch the car for anything more than it needs
2) Nobody makes a mistake because they don't want it coming back for a redo
That way it gets only the required maintenance. Nothing more, nothing less.