Yield might be the problem.I think you are still missing my point.
If I am am selling 3 chips, A, B, and C in my XYZ family, with the only difference being A has 32K of memory, B has 64K, and C has 128K, the C chip could be used by customers who need any of the 3, but the A chip can satisfy only the A customers. It makes sense to me to only make the C chip.
And @MrSalts, do you really think takes longer or costs more ti make the C chip? Often, the different versions actually all have the same die but parts of the chip are disabled for the cheaper versions.
Bob