Most — if not all — presidents ran for office because they thought they could run the country better than the other candidates. And running the country means being in charge of the US government. It implies some regard for the institution that would be paying their salary.
But Donald Trump never really considered the presidency to be a job. It was just a vehicle to gain the most attention from adoring crowds, obtain the best perks, maximize his brand, and hold the greatest power.
All his life, Trump has turned his back on government, declining to serve it in the armed forces, to follow its laws when they lowered his profits, to pay taxes to fund it, and even to speak well of it.
He lives in the kingdom of the gated community and the lush golf course, which could be anywhere or nowhere. He welcomed Russian oligarchs, Saudi princes, and mobsters to Trump Tower. The lingua franca of this kingdom is wealth and all its trappings. Nothing else matters.
All his talk of America First really is Trump First. He has no understanding of this country, its history, or its values.
So it’s not surprising that a shutdown doesn’t trouble him. He shut down on government and country a long time ago.