well, true, but this doesn't guarantee a node to stay in production. fabs sometimes shut down a node to use the equipment and space for another node with more demand. also, sone of these machines from 80s and 90s are simply old and it's not financially viable to buy a new machine for such a process. they typically cannibalize some of the machines for parts, or even buy old machines for parts from other fabs closing down. I believe a fan requies refreshing and investment every 15-20 years.