He didn't move up when he should have about 2 years ago, and now he's just too big to dominate at MW, he's looked clearly drained at the last few weigh ins, a sign of struggling to make weight. He should've moved up and took on SMW or LHW, yet he stayed at MW and tried to bully the smaller fighters yet ended up taking a big L last night. Canelo was the one moving up for this fight and performed well in a new division.
Same thing happened to Hopkins to be fair, by the time he got to 40 he was drained and slowed enough to be vulnerable. He moved up to have success against bigger slower fighters, no reason GGG can't do the same, especially as super middle is hardly a dearth of talent right now. I see GGG wrecking the 168lbs division if he moves up.