GF doesn't have the scale-at least not in the smaller nodes

They dropped out of the leading-edge logic race after getting to 14nm. Development and capex just got too expensive to pay off. I don't know much about the industry but it has been consolidating for 3-4 decades so it's probably just the same story, the up-front costs keep growing. I guess GF and UMC were approaching the limit of DUV where you start either having to do very complicated and expensive multi-patterning, or even more complicated and expensive EUV, so maybe that is what stopped them.