Because Trump's essential appeal is to hatred and despair; that's how he got the nomination and the election.
His appeal "was" to hatred. Past tense. The campaign is not the governing. Historically there is a very pronounced demarcation between the tone and manner of the behavior of the campaign and that displayed while governing.
Surely someone as clearly learned and well-studied at you would know that, sieur!
Isn't it also ironic to some degree, that those who complain about Trump using hatred as a strategic tool during the campaign are now employing the same to stultify and damage his reputation - and apparently without a trace of misgiving or remorse. Interesting.