Outside of things like grip, neck, low back, abs, strength training has diminishing returns. Strength training deals with overload and adaptation. In BJJ, you pretty much never deal with overload after a point, because everyone has to weigh in at the same weight.
Diminishing returns are not always purely physical. The mental drain of spending lots of energy for very low yielding return can really fuck with your motivation. Seeing as Rafa took a long break and has kids with legos all over the floors, a nagging wife, and having to constantly replace 800 watt blinding white lights at his academy, the stress and time to gain a little bit of strength he most likely will not need to win the competitions he is entering isnt really worth the pain in the ass.
Now, someone like Cobrinha, he is stronger than most guys he will face. Why does he continue with strength training? Because the physical gains might be diminishing returns, but the mental attributes he gains would be devastating for him to lose if he stopped lifting. I could be wrong about that, I dont know Cobrinha, but I know guys like that. Every guy has a few things they do to really boost confidence.