Wanderlei has never shown great BJJ, even in his prime. Partly, it's because of his fighting mindset.
Jr. Do Santos is another example. He was supposed to have a competent BJJ game, but he doesn't use it, even when he's outmatched on his feet.
Aldo could have mixed up his game more against Holloway, and tried to use his ground-game, but he is a real black-belt. He's just stubborn.
Some guys get their black-belt, but get KO addiction because of the ease with which you can earn a KO, and the marketability of going for it.
But we have to be honest, some guys were given their black-belts far too soon, and without as much effort as what guys normally put into obtaining a true competitive black belt.
Sometimes this is done in order to associate themselves with a well-known MMA competitor.
Rashad Evans is an example of an MMA guy who was given a black-belt for promotional purposes. He didn't even earn it in a gi, and I doubt Wanderlei did either.
You can train BJJ, and become good at it without pursuing a black belt in the gi, but it doesn't mean you should be given rank.