I turned out that this was due to a residual "magic number" from when I dd'd an iso image onto the disk (instead of onto a USB drive as I intended) a while back. For some reason, graphical tools like blivet, the old anaconda disk partition tool, and gparted picked it up and identified the disk as an iso9660 image instead of using the gpt partition table as command-line tools like fdisk, parted, and testdisk did.
I was able to fix it using sudo wipefs -t iso9660 /dev/sdX (credit)