USB is on same "OSI model" layer as PCIE is. SATA is not.

PCIE sata controllers in m.2 ssd are a thing, as are m.2 direct sata ssd, as are sata controllers on m.2 card with sata connectors capable of connecting 4-6 disks ( ASM1166 ). so i do not seem to see point you want to make there

sata -> memory card is solution for embedded market of 2000s not today, for refurbishments or efforts to keep using old embedded stuff. and again it has nothing to do with guys point, it is absolutelly different use case. he is talking about servers, ( servers with a lot of drives have expanders ) ! ! ! ! M.2 NVMe to CFexpress Extender is something else entirely, so depends highly on what EXACTLY are we talking about ! ! ! !

simple reason why it is nonsense - how much does 256 GB m.2 ssd cost? so just use that.

or use M.2 to PCI-E 4X 1X Riser Card ( adt-link K42ST ) and connect standard ubiquitous SATA/SAS/NVME HBA/RAID card into it and use any freaking disks.

or

M.2 Key M to SFF-8643 and use cable to connect it to something like H3platform Falcon 4118... which is "just" PCIE switch + psu + connectors.

or

m.2 to pcie connector and use HBA with optics to connect to 5 miles remote ARRAY.