Ah, but the car companies have already expended that capital. The problem here is they will have a lot of building capacity from all the factories they own, and possibly less to build with that capacity. There's nothing stopping them from buying extra needed capacity from another company, but in the meantime it may help them fill the lack of utilization they may see. At some point, some factories will need modernization as normal, and they can choose at that point to reduce factory capacity.

The point is that it's a possible strategy to get them from point A to point B when they've already banked heavily on certain future production trends if they've overestimated.