Thanks to everyone for the thoughtful answers. I wish I was insightful enough to have thought through the scenarios that percolated up in the replies.
Why question was much simpler and to this point: We often think "SSDs are basically the same building blocks as RAM; therefore if we put something on a SSD it will be as fast as RAM".
As you point out, THIS IS NOT THE CASE. Bandwidth to memory vs SSD, also write latency speeds, DRAM is constantly refreshed and thus has a latency measured in nanoseconds, often SSD latency is measured in microseconds.
I was having a conversation with our infrastructure guy, and he kept saying "Well, everything is going to be on FLASH anyway, so it really doesn't matter".