Well he almost did a perfect LGC couple of times this season.
The thing is, the Worlds took most of his strength, physically and mentally. And it wasn't even a normal WCh. Two time runner up then much worse, he had the injury, the unknown, then the break, the slow recovery, where they thought he might miss the season, then the fight whether to add the 4Lo or not, then the struggle to see whether this was actually the right choice or not and then it all culminated at the Worlds where all this pressure got to a breaking point and then - it turned out all right! He was right to add the 4Lo, he was right to struggle with a 4 quad layout, it all paid off.
But then it's like someone pops a balloon, that giant release of tension, even if it is positive. You could see this at the Worlds Gala when he kept mucking his jumps, I think he was just wrung out and ready to breathe. Except he can't, now can he? Because there's this super fluff fun thing to do, yay! That isn't actually that much fluff but more forced torture. So I don't think it's that he cannot do it in a real competition, we've seen him almost get it. It's just that overall this season has been really difficult, and it should have ended at Worlds with him putting his feet up for a week or so.
Nobody can handle pressure of this sort indefinitely, and if he's suppose to have a I'm just so done with this moment, WTT was perfect for it.