CP/M‑386 is currently in the very early development stages.

    Full 32‑bit protected mode implementation with Ring‑3 TPA.
    Bootable via 3.5" 1.44MB floppy disk MBR or GRUB Multiboot kernel.
    Supports VGA text (0xB8000) and/or COM1 serial (9600/N/8/1, 0x3F8) consoles.
    No floppy/hard disk/CD/USB/network/sound/other drivers (yet).

That's not surprising. The page says the kernel is multiboot compliant, which means it can be loaded by existing boot loaders. Whether the kernel later provides a floppy driver is a separate story.

This is also pretty common even if you don't use multiboot. The I/O services exposed by the BIOS or firmware during boot may not be usable once the kernel has started, and thus the kernel has to provide its own drivers.