The RNG system is basically designed to keep you playing to get what you want so they can report how many people are putting numerous hours into Destiny and it looks good for their numbers. It works almost like a gambling addiction. They give you a little taste every so often to keep you coming back, or you see that friend of yours drop a Suros Regime in 24 Tiger Strike so you keep thinking to yourself if you keep playing the same repetitive strikes over and over again maybe you'll get a Suros to, or a Hard Light, or something cool, but you just keep on getting engrams that turn into nothing and blue crap over and over again. Or you might have a terrible run with the cryptarch and then all of a sudden one night 3 blue engrams turn into Legendary items or you get that one legendary that turns into an exotic armor piece, and that keeps you coming back even though you had 28 prior levels of cryptarch where you didn't get jack squat. There is always that carrot and "Maybe I'll get something good next match" etc. going on here. There isn't much content in this game so the only way for them to keep you playing and interested is to make the loot completely freaking random, and their definition of RNG is the worst I've ever seen in a game. There are plenty of RNG games where it is much better designed.