Where would they get dollars? Part of what makes selling to the US beneficial, besides the massive market, is getting paid in dollars. If the US didn't have the world's reserve currency, the tariffs would just be a fart in the wind. Reserve status insulates the US from the consequences and compounds them on other countries that try to "punish" the US.
And you'll always have holdouts who decide to play ball with the US, getting maximum economic benefit at the expense of the boycotting nations. There is more upside for defectors than for boycotters. And there are already a few nations that have dropped their tariffs.
A reserve currency is only useful when there is some level of trust and stability. That is not the case now. Currencies are just tokens, and they can be replaced.
There is more upside in the US, but not with other trading partners. Very few countries are self-sufficient, or can thrive with only one trading partner.
This is a money grab, and while in the short term it might look promising for the average American with all of the "investment" coming into the country, they shouldn't believe the hype. That investment isn't in them, or for them.
I don't claim that you don't have legitimate concerns or thoughts. I just want to get across that although the media portrays Trump as capricious and haphazard, what is happening is planned and deliberate. The more I have researched the actions and the people involved, because it's not just Trump doing it on a whim, the more clear it is that the "chaos" is planned. Unfortunately, it requires breaking the status quo to bring in a new economic reality that primarily benefits the USA, but can also result in prosperity for other nations.
Much of the current international trade is based on post WWII decisions that no longer serve the US or the EU. The abrupt change is understandably worrying. But it is not happening based on the caprice of one man. There's a plan.