My understanding is that because it's a very small sample, it's basically a combination of a subset of sine waves, and because we're very sensitive to the nuances of high-pitched sounds, even small changes in that space make a lot of difference. Every RNG seed produces a different sounding hihat, and if you don't reset it, it continues producing different hihats, which is unnatural. Another explanation is also to resemble sample-based audio, but perhaps it's all of these things combined.