The best explanation as to why ASML is so dominant is that they have locked out the best suppliers by signing exclusivity deals with them. If you want to compete with ASML you have to vertically build: the best lenses, the best lasers, the best metrology. A new entrant would need to replace ten different world-class vendors simultaneously.
Unlike common business wisdom that dictates having multiple suppliers to mitigate risk, ASML succeeds by identifying the best supplier in the world for each critical component—such as Zeiss for optics or their specific metrology group—and securing exclusive, multi-year deals with them.
Dan Gelbart gives exactly this view in a podcast he took part: https://youtu.be/UTgrWmOk4q8?si=Zp13SPqN_Vx-kFlq&t=1564