https://www.selectusa.gov/financial-services-industry-united...
What's the size of the financial sector of Luxembourg or Switzerland?
Well, actually, since you brought it up ...
The SNB has been buying euros, and other currencies (selling swiss francs) since 2011 in an effort to depress its value, which they believe is too high and hurts their exports.
Here is a decent summary of the events leading up to their interventions and the current scenario:
https://admiralmarkets.com/analytics/traders-blog/price-shoc...
In summary, the CHF is viewed by many market participants as a safe-haven, or reserve currency (especially in Europe) and the Swiss National Bank has been acting, unilaterally, for many years to manipulate the CHF downwards in value.
The USD is the world's reserve currency because we have a balance of being the largest economy with a fair rule of law, lots of real estate, 50 competing states, natural resources, and the manufacturing expertise that means if anything goes super wrong we're the best place to be.
Luxembourg and Switzerland also have a history of being tax havens.