Do you really think the US spends all that money for nothing? It gains them power, hegemony. In the case of the defence industry, it enables them to be the biggest seller to NATO. Billions of dollars of sales.
Now it is pulling back, and proving to be unpredictable and unreliable, those NATO countries own defence industries will step up their own development and sales. just like the South African and Israeli arms industries did and those sales will disappear.
The rest of the world is far from perfect. I know, I am British. You only have to look at the state of my country. I actually agree with some of Trump's policies, but what he is doing, and how he is going about it is absolutely crazy.
Destroying friendships and alliances, talking about taking over sovereign countries, tanking the US stock markets, getting China talking about war. ignoring judges and overriding the judiciary to say thee least does not seem a good way to go about things..