You might want to look at your front forks. If you're heavier than like 155lb, you might want stiffer forks and thicker oil so that the front doesn't dive on hard braking.I had at least 3 to 4 cars worth of distance. That gets eaten up quickly if someone brakes card though I should of uploaded the video that has the GPS on it. I went from 65 to 45-40 before the hit. Why did that guy break that hard? Was he avoiding something? I find it hard to move the bike when breaking, I don't have this issue as much on my ninja 300. But I think I will take your advice and practice hard breaking again. Last time I did that on the freeway, the rear end came forward. Terrifying I was lucky the bike didnt throw me over.
Other than that, it's really worth to go out and practice emergency maneuvers so you know how the bike will react and how hard it can be pushed.
As far as why they would brake so hard, who knows, maybe they saw a duck in the road, or looked up from facebook to remember they were driving and panicked. You have to read the traffic. You can usually tell who the bad drivers are, and stay away from them, or leave extra room and cover your brakes.