It has been pointed out to me when I say this that you cannot just switch a fab designed for VLSI gates in CPU into giant RAM making machines: The fabs all have their own peculiarities. They need to be tuned. Nothing is free, nothing is quick. The number of layers, the reagents, the specific dopands, they all vary. And contamination would be a real problem at this scale so purging a line made for process-A chemicals to become process-B must be quite an exercise too.

I believe current RAM and SSD stuff is very multi layered too. The older lines might just not "do" that amount of stacking.

(Not a VLSI engineer or a brain surgeon)