I dunno, maybe because he's the chief executive of the US federal government?

They need this carefully crafted image in the media of a stupid and crazy maniac.
His adversaries can underestimate him and he can get out of difficult questions simply by talking gibberish.
More importantly:
In the short term he's president he can act like a loose cannon, make wild moves that wouldn't be possible under a rational president.
Even against ~~partner~~ vassal countries.
And in 2 years they can blame it all on him, of course they will not (be able to) change the beneficial things for the powers behind the curtain.
The next face will definitely apologize for stealing oil from Venezuela, etc but explain the situation is changed now, contracts with oil companies signed and more excuses to keep this situation in place.

Every 3rd rate celebrity has people to manage their many social media accounts.
Do people actually believe he's coming up with all the crazy tweets or messages?
The 'I have all the cards' one is obvious.
They chose this game specifically.
As if there's nobody in his media team that knows how to play UNO and would let it pass.
I am not buying the act.