Both TSMC and ASML are just the tip of an iceberg. Each has thousands of supplier companies spread across many countries. Many of these supplier companies are peerless themselves in their respective areas.
It's a lot less concentrated on those two countries than it seems, but at the same time things are even more fragile than your post would imply.
The lithography/EUV optics comes from Zeiss. The laser for generating the plasma from Trumpf. Both key elements that ASML would not be able to build in-house or get from a different supplier.
There's a lot of expertise with lithography around the world too (companies like Canon build lithography machines), but we're not talking the usual levels of it.
The EUV lasers ASML/TRUMPF builds don't even work the same way other "conventional" lasers would[1]. You physically can't get there by incrementally improving some existing process. Now I don't know how ZEISS makes mirrors that blown up to the size of a country would have imperfections smaller than a human hair, but I'm pretty sure it's no small feat either.
These companies invested decades and untold sums into this when few other companies even had incentive to attempt it themselves. Sure, other companies could eventually replace them, but you're not closing a 2-decade technology gap in an afternoon.
[1] It's a bit insane, really. Vaporizing falling droplets of tin with two laser pulses 100,000 times a second to get just the right wavelength? Here's a good video: https://www.youtube.com/watch?v=5Ge2RcvDlgw
It is impressive for sure, but still a lot of other things are. Mirror arrays on JWST, fusion ignition lasers. Diffraction limited optics aren't exactly last year development either: there's a host of other places across several countries who can match Zeiss for what is essentially bespoke builds.
> there's a host of other places across several countries who can match Zeiss for what is essentially bespoke builds.
Ah yes. No development time involved here at all. They just built it. I don't know what ASML, TRUMPF, Zeiss, and occasionally the Fraunhofer Institute were mucking about for 25 years. Completely boring bespoke build. Bah. Could get it from anyone else by next week. Pick an off-the-shelf coating too and be done.
It's a wonder nobody else is taking a slice of those ~4 billion USD of revenue Zeiss is making off a bunch mirrors for lithography machines each year.
There’s always these weird bottlenecks in the supply chain though.
My favorite example is during Covid where reduced boron quantities resulted in less Pyrex glass that makes test tubes meaning transporting vaccines was at points rate limited.
I’ve read similar points in the components for lasers to ASML but can’t remember specifics. Chip shortage is the funny one, ASML require more chips that limit their turnaround times which in itself limits chips.
It's a lot less concentrated on those two countries than it seems, but at the same time things are even more fragile than your post would imply.