Chinese SSD Manufacturer UNIS Flash Memory Unveils World’s Fastest PCIe Gen5 SSDs, Featuring Speeds of Up To 14,900 MB/s

One of the biggest bottlenecks in many workloads is latency. Cache miss and the CPU stalls waiting for main memory. Flash storage, even on an nvme bus is two orders of magnitude slower than ram.

For example L3 cache takes approximately 10-20 nano seconds, ram takes closer to 100 nano seconds, nvme flash is more than 10,000 nano seconds (>10 microseconds).

Depending on your age you may remember the transition from hard drives to ssds. They could make a machine feel much snappier. Early PC ssds weren't significantly faster throughput than hard drives (many now are even slower writing when they run out of SLC cache), what they were is significantly lower latency.

As an aside, Intel and Microns 3d xpoint was super interesting technically. It was capable of < 5000 nano seconds in early generation parts, meaning it sat in between DDR ram and flash.

You want RAM because you don't want to have your computer store and constantly read/write to through TBs of temporary/useless data constantly. You need a form of cache for even faster read/write times.