They didn't really. What this wants is gobs of memory bandwidth. The fastest NVMe SSDs can essentially saturate the PCIe bus. Using a dozen or more of them in parallel might even have reasonable performance for this. (Most desktops don't have this many PCIe lanes but HEDT and servers do). And they're a lot cheaper than Optane was.

To do better than that would have required the version of Optane that used DIMM slots, which was something like a quarter of the performance of actual DRAM for half the price.

So you had something that costs more than ordinary SSDs if your priority is cost and is slower than DRAM if your priority is performance. A lot of times a middle ground like that is still valuable, but since cache hierarchies are a thing, having a bit of fast DRAM and a lot of cheap SSD serves that part of the market well too.

And in the meantime ordinary SSDs got faster and cheaper and DRAM got faster and cheaper. Now you can get older systems with previous generation DRAM that are faster than Optane for less money. They stopped making it because people stopped buying it.