To expand on this, RNG without clumps/streaks would be bad RNG because the lack of streaks would mean that the system of RNG is taking into account previous attempts and augmenting your next attempt in order to keep the results constantly close to the displayed amount. In other words, your chance of success will increase if you had bad luck and decrease if you had good luck. This adds a pattern to the RNG, thus making it less random and a bad system of RNG.
In a good system of RNG, the chances of every single gather attempt is taken in a bubble. Your success and fail rate history don't matter. Your previous gathering attempts don't change the chance of success of your next attempt. No matter if you've been having a good luck streak or a bad luck streak, the chance of your next attempt is still the displayed value. This "each attempt's chance is taken in a bubble" is what will result in streaks, and it's a sign of properly implemented RNG.
Edit: Note that what I mean by "good" and "bad" RNG is how true to being random it is. I'm not saying it's a bad thing to implement an augmented RNG system, only that it's "bad" in that it's not actually random.
