Surely when people point out Trump's faults it's not in the hope or expectation of changing him, that would be silly.

Pretty obviously those character failings are a major part of what has got him up to where he is. (And may serve to ensure his fall in time.)

The reason people might go on about them is to encourage others to see them for what they are, and see him for what he is, and maybe to be repulsed. That may be pretty hopeful so far as most of his supporters are concerned, but it's not irrational in itself. And it might help nibble away at the edges.