Closer to furlongs per hour :)
It's a convention.
Maybe back in the day when 300 bit per sec was the norm, nobody ever thought they'd need to be working with kilobyte sized files. :)
I've seen a steady progression in download speed from 300 b/s - 1200 b/s - 2400 b/s - 9.6 kb/s - 14.4 kb/s - 56 kb/s - 256 kb/s - 768 kb/s - 1 Mb/s.
At one point to you change from bits to bytes without making it look like you lost something?
Could be worse, could still be using baud rates....