Comment by klodolph

I am guessing a combination of tighter manufacturing tolerances, smaller sector sizes, and manufacturers over time cheaping out would contribute to decreased reliability of 3.5" disks. People also, as far as I remember, universally used sleeves for 5.25" disks, but almost never had cases for 3.5" disks.

On the other hand, 3.5" disks have higher magnetic coercivity, which makes them less susceptible to data loss from stray magnetic fields (e.g. nearby motors).