Aye, FW was mostly popular* because it wasn't polling-based, and thus was more reliable than USB in high CPU load situations. Now USB 3 is interrupt-driven too, the gap is narrowed in that respect- which means Thunderbolt is still something of a minority pastime outside of Apple land. Cost of implementation/licensing often trumps other considerations for most gear. (If you've ever seen any of the miserable megathreads about optimising Windows/MacOS to avoid USB buffer underruns for live performance use in Serato/Traktor/Ableton, you'll feel the cost in stress of the cheaper approach of USB and USB 2.) * Obviously, the raw throughput was higher, too- but that was rarely the main issue for audio.