Intel cant use their own fabs (ie F42) why would they want an old non-CE! Fab? They already close all other aquired fabs (Colorado and Mass.) Been there before. Tech, patents, and an opportunity to disrupt the GloFo/Samsung alliance as a reason, thats another story.
Fishkill Fab is mostly development FAB ( R&D) and plus a little bit capacity for running older ASICs and about not much wafer capacity for a legitimate foundry business, besides global already has decent size fab in upstate NY.
Yorktown is a pretty big R & D center and not just for Semiconductors. Everything from Software, servers, devices, physical sciences,Mathematics is reserached there.
Silicon and semiconductor research can't really be done without a FAB like facility.
IBM was already making X86 based server (which we call comodity servers) which was made using latest Intel technology, which they sold to Lenovo, and these server sold at cheaper prize than servers based on IBM chips,
So it look like they can't sell their servers using generic chips.
IBM uses its Semiconductors Tech for its servers, that gives it advantge in high end servers, once they sell their semiconductor business this high end Server business will go as well.