alt Hacker News[not an expert so I could be totally wrong] I was also just talking about the physical space. Even if the machines on the entire line have to be replaced it still probably makes sense for a company to transition in situ - displacing the old line. There's the lease for the land and building, people's commutes are structured around a certain physical location, air conditioning and electricity are already there, etc... It's not just the big expensive machines that make up the fabrication - it's also the entire structure that makes that production happen.
Even if they need to replace every single lithography machine, there are a lot of other machines that probably don't need to be replaced for any given upgrade.
Like everything related to it being a clean room; All the logistics robots which move wafers around; All the machines that deposit layers of material like CVD/AVD/Sputtering; The various machines that do the actual etching; The furnaces; The inspection and quality control equipment;
Also, absolutely everything to do with dicing and packaging. But that's usually already at another factory (often a completely different company) due to how process agnostic it is. Same applies to growing and prepping the silicon wafer.