It’s because it’s the first time he’s looked vulnerable which makes any person relatable, and human, to others. The Tulsa rally was a bust, his poll numbers are down, he’s so out of touch everything that previously worked for him is backfiring spectacularly, he seeing the writing on the wall of a defeat in November of his own doing. His preciously fragile ego has to cope with the idea of losing, for the first time, and on an epic, national scale like a Presidential election. But we all know he won’t learn anything and this opportunity is wasted. He’ll blame any one of a number of outside forces, as he can’t look internally and accept the blame, move on, and grow. He has no empathy for anyone, not even himself. That is why we look on him like this with pity, because that is the real tragedy of that man’s life: he’s an utterly failed human being that plays a child’s game of pretend through scorekeeping things that are hopelessly trivial yet calling it being successful and “always winning” and oblivious to the real trauma it causes others. TL;DR Trump is every failed coping mechanism in a 3-piece suit pretending to be an adult.