The pure marginal cost of fabrication of a modern chips is not that cheap when seen in the context of production capacity (and with high demand you tend to concentrate on high-end anyway), and certainly not cheap compared to software, otherwise you would have even less kind of dies than you have today for the various SKUs, and less recovery strategies for various fabrication defects, plus Intel wants to fab for others, and they do not lead the process anymore. Also if you look at their current list of SKUs, that's already completely insane. Do they really need further discrimination on top of that and will they be able to extract tons of value? I'm not so sure.

Thinking more about it maybe they simply want to keep roughly the same amount while doing less masks than usual because masks became crazy expensive. Would be interesting to look at some figures.