There must be some functional purpose that I am not imagining here ?
There are plenty of devices that were built when 3.5" drives were the de-facto standard and are still in use today, e.g. lab equipment, mixing desks, digital signage systems, etc. These pieces of equipment are often too expensive to be replaced purely because you want shiny new stuff that does the same job, but the lack of newly manufactured 3.5" media and drives means they are becoming less and less maintainable and degradation of existing 3.5" media can risk loss of functionality. An FDD emulator means you can use newly manufactured interface hardware, commodity storage (e.g. SD cards), and keep media backed up with replication in the event of loss, damage or failure being trivial.
Plus, old PCs used as retro toys, I guess.