

The main point is that the disk controller gets exponentially more complicated as capacity increases and that the problem isnt with space for the nand chips bit that the controller would be too power hungry or expensive to manufacture for disks bigger than around 4tb.
USB ssds seem to have a lot of weird issues being used for a nas drive. Sometimes its a power management thing on the SSD itself, sometimes its something odd with the USB controller on the host. Occasionally the power supply of the sff pc doesnt have enough amps for all of the peripherals. Using an intermediary like a usb hub makes all of these issues worse since you add another device with its own potential conflicts.
Not to say its not possible to do, but USB drives and NAS’s rarely play nice together.