Cuz PC doesnt "NEED" that, PCIE by definition is either talking directly to the CPU already or to the chipset.
With new IO solutions the CPU can even be bypassed entirely....why would we need something else to "talk" to the SSD?
The IPC of a full fat CPU/GPU is enough to not need to have a separate piece of hardware to do the decompression.
And once the Win 10 version with DirectStorage is out, devs will just force that version as minspec and the war is over.
Hell they could put an SSD in the rec spec as well to make sure their game works correct.
HDD for minspec but dont cry if the game runs like shit on your PC.
In a gaming PC you are going to have a GPU or CPU thats vastly superior at decompression instructions than the chip in the PS5 so why would anyone want to then have another custom chip to do that job, just schedule a core/thread or the GPU to do the job.
So yes you are correct there are no consumer level custom chips for I/O and decompression.....in the same vein on PC there are also no consumer level custom GPUs, or custom CPUs, or custom RAM configurations, or custom SSDs.....see where im going with this.
DirectStorage might be alot closer than you think.