By your logic shouldn't we already have a single global currency because that is where we would logically converge to?
The world has been trying to converge to a single global currency for many decades. It takes concerted effort by national governments to resist this pressure.
A free market would converge to a single currency.
What I think is that you are implying the convergence to a monopoly, a single globally accepted digital currency.
If you're using the word "monopoly" you're thinking of this in the wrong terms.
Currencies are communication standards, like alphabets, or numerical systems, or the metric system, or charging plugs for mobile phones.
Competing standards introduce friction, which the market continually works to erase.
This is a widely observed phenomenon.
I don't think it is in the nature of humanity to agree. There will always be people wanting something else
How nice for you.
Hint: Maybe try something some epistemology?