[dnanian]

Specifically, FW maintains speed bidirectionally, and doesn't 'step down' its performance to very low levels when slower devices are connected (because each drive is at least FW400). Bidirectional transfers (read and write) can occur simultaneously, too, at full speed.

On top of that, each FW device is 'smart', and transfers between devices are handled by the device, without mediation by the host.

FW 'power' is more reliable and higher, so bus powered devices tend to operate better.

Because there are 'more' devices with USB connections, there are more opportunties for bus disruption, slowdowns and failures.

Finally, a FW port is a FW port. On laptops and the like, some of the USB ports are 'high power', some are not, and users can get confused. (Yes, there's FW800 and FW400, but they're explicity different ports, even though you can use an adapter.)

No doubt there are many other reasons, but those are some off the top of my head.