Most of that effort was to ensure the processors could actually ingest data at the speeds that off the shelf SSDs could deliver it. The Xbox Series X shipped with what was a low-end NVMe SSD at the time, and the PS5 used a custom SSD controller primarily so they could hit their performance targets using older, slower flash memory rather than being constrained by the supply of the faster flash that was just reaching the market at that time.

And there are still hardly any games that even make a serious attempt to use the available storage performance.