SSDs have become fast, except in the cloud

The fastest SSDs tend to also be MLC which tend to have much lower write life vs other technologies. This isn't unusual, increasing data density generally also makes it easier to increase performance. However, it's at the cost that the writes are typically done for a block/cell in memory rather than for single bits. So if one cell goes bad, they all fail.

But even if that's not the problem, there is a problem of upgrading the fleet in a cost effective mechanism. When you start introducing new tech into the stack, replacing that tech now requires your datacenters to have 2 different types of hardware on hand AND for the techs swapping drives to have a way to identify and replace that stuff when it goes bad.