I disagree.
My buddy has a mechanic business, works on daily drivers, builds performance engines, and several sprint car motors. He's seen it all. Some are just bad maintenance but, even where people have changed the
oil religiously, some have sludge. Some racing oils don't have detergents.
Is it the brand ?
Has the
oil got too hot, to many times ?
Extreme conditions ?
I don't have the answers, but it happens.