While in absolute terms memory access has gotten faster, in relative terms it is MUCH slower today, compared to CPU speeds.

A modern CPU can perform hundreds or even thousands of computations while waiting for a single word to be read from main memory - and you get another order of magnitude slowdown if we're going to access data from an SSD. This used to be much closer to 1:1 with old machines, say in the Pentium 1-3 era or so.

And regardless of any speedup, the point remains as true today as it has always been: the more memory you want to access, the slower accessing it will be. Retrieving a word from a pool of 50PB will be much slower than retrieving a word from a pool of 1MB, for various fundamental reasons (even address resolution has an impact, even if we want to ignore physics).