Shrinking silicon has paid off thru the years. At some point it will be more expensive to go to the next step than to stay where we are. That is why companies band together to get there. Sharing the cost can help to make it more economical.
This makes sense for both companies. For a long time now IBM has been selling its process development knowledge to others as a revenue source. It's part of their move to a "services" company. At the same time SMIC has had difficulty keeping up with the latest technologies. They hope to buy the process from IBM as a way to close the gap.
I agree that this is a good deal for SMIC, especially since whatever cost involved will not have a material impact on the company's technology. But IBM is partnered with so many foundries through the Common Platform Alliance (Samsung, Globalfoundries, UMC). I wonder how they feel about this.