The "R" in RNG is not equally weighted. For a simple example: if there were only 10 total exotics in the game, and Hawkmoon was one of them, one would expect to get one on average every 10 drops. But if the system is rigged so that Hawkmoon only has a 1% chance of dropping, and the other 9 a 11.1% chance of dropping, they can keep you chasing it for a long time. Then, once you get it once, the odds to get it again can be reset to 10%, enhancing your odds of getting it again sooner. So while it is still random, the system is rigged to keep people chasing longer.