Using a national currency as the de facto global reserve guarantees a trade deficit for that country. No one else can manufacture USD's, so other countries have to acquire them by shaping their economies to supply goods and services demanded by the US. They can then use these earned dollars to transact with other countries, as the US itself insists they do. For the US, this is a simple trade off - gain massive politi…
USD has mostly been where it is because the alternatives are a lot less appealing:
* CHF - they explicitly would rather not be a strong reserve currency and threaten to print money whenever it starts strengthening
* JPY - they also don't want a strong reserve currency because it would tank their export led economy, plus Japan's debt and economy make the US look very healthy in comparison
* EUR - people remember the Euro crisis, and a lot of the fundamental issues with the currency were just papered over. It wouldn't ake a lot for a new Euro crisis to happen.
* GBP - post Brexit, not that attractive, and not so long ago the whole Liz Truss debacle happened to the currency
* CNY - China flirts with the idea of a reserve currency from time to time but would much rather have the ability to impose strict capitol controls quickly
It's only in the last year or so that USD has started to look very wobbly.