Why neither Asia nor the US has produced a rival to ASML

It’s hard and not economically viable to catch up:

“Powerful lasers are fired at microscopic droplets of molten tin, turning them into plasma hotter than the surface of the Sun. That creates a pulse of extreme ultraviolet light, which is then reflected off a series of mirrors, each made with atomic-level precision and taking months to make, before the pattern is finally transferred to the silicon wafer. The hardest part to replicate is the optics. EUV-grade mirrors are produced by a single supplier: Carl Zeiss SMT. They are the product of decades of tightly integrated development between Zeiss and ASML. Even if a peer could replicate that technology, the economics do not work. Any new entrant would sell too few machines each year to recover development costs, yet those machines would still be expected to deliver near-perfect reliability from day one.”

Patents?