The old 8” floppy disks were more expensive but known for being incredibly reliable.
The newer 5.25” and 3.5” floppies used cheaper and mass produced coatings on the magnetic surface, plus the smaller and higher density tracks had less surface area per byte and less material to hold the signal.
The net result was the newer floppies often couldn’t be reliably read after a few years of use.
It’s not at all surprising they stuck with the more reliable system for so long.