One possibility I sometimes consider as a joke is that the people who seriously deny the existence of the hard problem might just actually be philosophical zombies, totally lacking in any conscious experience of their own. This is reinforced by, e.g. Dennett writing a whole book in which he alleges to explain away the problem, but instead spectacularly ignores it altogether. It’s almost as if he doesn’t even have a clue as to what people like Chalmers are talking about.