We're not talking about nanoseconds of real time; we're talking about nanoseconds as measured by the CPU doing the processing. Nanoseconds are not likely to be a uniform variate.
Note it's not that number, but roughly the square root of that number, that matters.
And they might be quite non-uniform. If the scheduler tick and the nanosecond clock are synchronous, you could end up with a few thousand popular values instead of a billion.
It's not a real concern today, and probably won't be a real concern in 10 years, but it's not so far removed from possibility that no one has to think about it.
