[monocasa]

They're not really taking up space per se. For the cost of a fab, a new building (or new wing of a building) is peanuts.

Adding on to that, in a lot of ways the fab is the building, and at a bare minimum you'd be resetting a lot of the yield issues you fixed by moving it to a new space. So then you'd be left with an old node and yield issues, and what's the point of that?

There's also a ton of trade secret style IP still in the old nodes that could help a competitor, so why let it leave your property? Intel for instance is so into preventing trade market theft on the specifics of their nodes that they (at least used to) manually drill out every mobile device camera allowed in their fabs, in addition to the normal "no outside electronics past this point" security stations.