I don't think you get how specialised these facilities are. They can't convert from one process to another, for the same reason they can't just build a new one on the new process. The physical building is not even slightly the bottleneck. If they can afford a new process they can afford a new building for it.

There's a story where a fab company tried to open a fab in America but the chips kept coming out broken, and they tried everything and the only thing that worked was disassembling the whole factory and rebuilding it in the exact floor layout of their Taiwanese one.

Sometimes they do salvage one or more machines as both processes use the same one. But that had better be worth shutting down the old process, financially.