You might be missing that you cannot just "port" across fabs.
Intel doesn't have demand because they only make Intel chips, and they haven't been doing too well lately.
I think realistically you wouldn't port the exact same design between manufacturers. That would be a waste of money unless one manufacturer is really rinsing you.
More likely you'd switch manufacturers when you planned to switch process nodes anyway, in which case the increase in workload probably wouldn't be too bad.
They do it all the time when they change nodes.
It is not that it cant be done. It is not reasonable or cost effective to do it without some clear incentive.