Other people point it out, but what you'll notice if you pay attention is that everybody seems to have rolls that they get frequently, but those rolls are different in every case. You could make the argument that bungie just decided to make certain rolls more common for each person individually, or that they [i]somehow[/i] have an algorithm to figure out which specific roll you want and make it so it doesn't drop for you, but I think that's a bit of a stretch. Like, it's possible that the perks are weighted, but given the difference in each players experience on which ones are weighted and how heavily, I think it's more likely that people are getting unlucky and cognitive biases are doing the rest.