IIUC, CFExpress is just a PCIe interface in a different form factor, so the adapter in the post should basically just be a pass-through. Conversely, a USB-C adapter would require some level of protocol adaptation/electronics/etc.
Plenty of USB-C SSDs on the market are actually M.2 in a trenchcoat, e.g. the nice looking black and orange SanDisk: https://www.reddit.com/r/hardware/comments/9631os/sandisk_ex...