If media is poorly manufactured it may contain a substantial amount of debris that might be caught by the liner during duplication, then later become dislodged and eventually scratch the disk. Or, a customers drive might reside in a dirty environment or receive infrequent use and subsequently have dust build-up on the drive heads. Diskettes contain a substantial amount of data written in a very small area. All of this requires precision in both the write cycle and the read cycle. Software manufacturers can control the write cycle, but the read cycle is beyond the control of everyone except the end user.
Diskettes are extremely sensitive to magnetic fields.
Most shipping companies are cognizant of this and try to avoid exposing electronic media to harmful devices. However, mistakes do happen. Media, like most materials, is affected by temperature. When exposed to extreme heat or cold the media will expand or contract. If the media is immediately written while it is in this temporarily modified state the data will be stored in an area of the disk prescribed by format specifications.