Political optics. Current POTUS's claim to success rests, in part, on a high performing financial sector. If the market tanks or stagnates, he no longer has that as a talking point.
If the market tanks, all the talking heads will just blame the upcoming election, and claim that markets and market makers are scared of a Democrat being elected. It doesn't change the talking points for the President at all, I imagine. He still claims the moral victory, if only he hadn't been undercut by those thieves on the other side.
That sort of thing is standard now. Claim success until you can't, then deny any involvement and blame someone else. That's politics, baby.