Why is Trump so feverishly crowd size obsessed?

I can't understand why crowd size, and people walking out of his rallies early, is such a delicate subject for him and one that he can't ever stop talking about? 

Has anyone else running for president of the United States ever spent so much time talking about crowd sizes during an election campaign? 

I realize he doesn't have the intellect of an adult and that he's only driven by ego and emotion, but it's over the top how obsessed he is with the number of people willing to watch him babble on stage in some redneck part of the US for 90 minutes. He even compares his crowd sizes to Martin Luther King, which is so bizarre and completely out of context. 

Harris was actually able to bait him (with people leaving his rallies early) during the debate and that triggered him to start feverishly rambling about crowds again. He walked right into the trap head-first with his oversized narcissistic disorder. 

Then that interview on Fox, unbelievable, he talks about how the audience loved the debate, when in fact there was no audience present at all, and a total of only four people together there inside the debate studio. 

He's so deluded and crowd size obsessed that he even talks about crowds at an event when there wasn't even one at all.
 

In fact, only somebody in early stages of dementia would make a gaff like that. You can't make this stuff up. People should have to take a cognitive function test to qualify to run for president.