Back in the 1980s, I was doing a lot of flight testing on the re-engined 767 (CF6-80C2) - which was also the same time they were making carbon brakes an option. The test pilots had considerable complaints about the 'On-Off' characteristics of the carbon brakes and far preferred the 'feel' of the steel brakes.
Educated guess here (I'm an engine guy), but I suspect that newer models - such as the 777 - which were originally designed for carbon brakes have changes in the brake system to give better feel.