Where else would they park it? The stock market is being automatically pumped by 401k auto purchases and similar investment strategies that amount to basically a tax with lipstick to subsidize the market. I don’t think any other nation is pumping their own assets to this scale. Maybe china but they don’t exactly let in outsiders to milk a good cash cow I wouldn’t think.

Also, the primacy of the American banking system allows the US to use it as a cudgel against foreign countries to make them do do all sorts of things. If some other currency is the global reserve, we lose a fair bit of soft power.

There are a lot of reasons we like being in the position we’re in, and I don’t think we know how bad losing it will be, if we do, but I think it’s unlikely to be positive. (Clearly our economists have largely agreed or we’d have gotten here sooner.)