Because they know that Americans almost always elect a president who is the opposite of the previous president.
President Trump is an old, reactionary, incompetent, rather stupid white male without government experience.
Therefore President Not-Trump will be a young, liberal, competent, intelligent, female person of color with government experience.
Kamala Harris matches that description perfectly.
Hence all the drooling in the media since she announced her candidacy.
Of course, her experience is limited and her track record at least questionable, and we have little idea where she actually stands on issues. But to raise such questions would be a terrible distraction from the overwhelming, vague impression that she’s the right person for the moment, and that she’s a safe choice who can be counted on not to upset the status quo—not, in other words, to alienate the ultra-rich and the corporations and the Pentagon, as Elizabeth Warren or Bernie Sanders certainly would.
So there you are: President Harris.
Let us pray.