он разрабатывался просто с более жёсткими требованиями - isochronous real-time data transfer.
The original release of IEEE 1394-1995[15] specified what is now known as FireWire 400. It can transfer data between devices at 100, 200, or 400 Mbit/s half-duplex data rates.

Although high-speed USB 2.0 nominally runs at a higher signaling rate (480 Mbit/s) than FireWire 400, typical USB PC-hosts rarely exceed sustained transfers of 280 Mbit/s, with 240 Mbit/s being more typical. This is likely due to USB's reliance on the host-processor to manage low-level USB protocol, whereas FireWire delegates the same tasks to the interface hardware. For example, the FireWire host interface supports memory-mapped devices, which allows high-level protocols to run without loading the host CPU with interrupts and buffer-copy operations

т.е. как правило в PC стоит USB PC-hosts rarely exceed sustained transfers of 280 Mbit/s (а ещё чаще - 240 Mbit/s)
к тому же не грузит CPU, т.к. FireWire host interface supports memory-mapped devices.