We've got plenty of mechanisms (SWIFT, ACH, wire transfers) that work pretty well for large electronic inter-bank transfers
within the same monetary authority. The trouble is what happens when you want to trade between currencies.
Say that I want to buy a DJI drone, which is made in China. The workers who made the drone all get paid in yuan. I get paid in dollars. I want to spend my dollars on Amazon, receive a drone, and have those dollars automagically converted into yuan to pay DJI. Behind the scenes, Amazon takes my orders and my dollars, and has a contract with DJI to send them a certain number of yuan. Similarly, behind the scenes DJI is spending yuan to buy ads on Google.cn (hypothetically), which Google then wants to turn into dollars so it can pay my salary. Both Amazon and Google have relationships with banking institutions, so they say "I need to convert $X of dollars in CN¥0.15X of yuan".
The banks net out all the purchases made by Americans with the purchases made by Chinese, and then they need to trade on the currency exchange markets for any shortfall. On the national level, the shortfall is called the current account deficit, which has been persistently growing since 1991:
https://www.economicshelp.org/blog/483/economics/why-us-curr...
That article lists a lot of hypotheses for why the current account deficit has been growing for the last 30 years, but the primary one relevant to this thread is the dollar's status as the world reserve currency. This means a few things:
1) Historically, since WW2, the U.S. has been the most economically stable nation in the world, and so holding U.S. government debt is the most stable place you can park any excess savings that you get from a current account surplus.
2) Because of this stability, a lot of trade in other currency markets is denominated in dollars. Rather than trade directly between Iranian rial and Chinese yuan, Iran takes the dollars they receive for oil, pays China for infrastructure improvements with them, and then China converts the dollars into yuan to pay their employees. (In practice it's a bit more complicated because since 2015 China has been doing their best to reduce their dollar holdings, so now China might pay Caterpillar or Bechtel to build a road in Zimbabwe, with a contract that lets China take over the road if Zimbabwe defaults on the loan that funds it.)
3) Oil is priced in dollars, meaning that most countries on earth need to buy excess dollars in order to afford a fundamental energy source.
The dollar's status as a reserve currency means that the U.S. can get away with certain things that would cause other countries to default. For example, take the recent $6T COVID stimulus. Who's paying for that? It's literally holders of U.S. treasuries: all the countries that have sold more to the U.S. than they've bought and parked the excess in treasury bond purchases. They're not exactly happy about that, but the U.S. controls the world supply of both dollars and of U.S. government debt, so if you own either of those, you are at the mercy of the U.S. government's decision to print more.
This is where the trustless aspect of Bitcoin comes in. You know that the supply of Bitcoin is fixed. If you settled up your current account deficit in Bitcoin instead of dollars, you know that you'll have an asset that you can trade back at a later date, and that the supply of that asset will not have increased (devaluing your own holdings). This makes it very appealing to other governments who are sick of bankrolling Americans' propensity to consume more than they produce. It's potentially bad for Americans (though the effect of this is complex: it might actually bring manufacturing back to the U.S at the expense of the financial industry, because a major reason U.S. manufacturing is non-competitive is because the dollar is overvalued, which is because the dollar is the world's reserve currency), but it's good for foreign countries with a trade surplus, and for holders of Bitcoin.