ah, I got so absorbed by the "fastest open wheel motorcycle" thing, I dazed for the "one mile" thing.
still, even as a 1 mile thing, I think its mostly because no one was really trying. In my view the performance community has been so focused on dyno numbers (bikes that aren't even ridable running in contests), and on 1/4 mile performance, that nobody's invested the time and resources to focus on this thing. Since 475whp is not nearly at the leading edge of what these bikes are putting down, my guess is, anyone with the interest could have done this.
my suspicion is unchanged, which is that this is not something that other people were all desperately trying for and these guys succeeded where others didn't. I think just enough people weren't trying.