[wmf]

Since SRAM is physically larger most of the bits would be farther away and thus the speed of light would introduce some latency (3D can reduce that latency but at even more cost).

But I think the real reason SRAM is not used is because it's trapped in an expensive/low-volume local maximum and there's not enough demand to push it into a cheaper/high-volume state. Caches actually work pretty well.

[mmf]

Let me correct you here: it's not the speed of light the issue here it's the parasitic capacitance that grows with the size of the subarray.

From that point of view, when the array is large enough, the particular technology you adopt has only minor influence on the access time.