Or maybe, just maybe, the chance of you getting the exact weapon you want is just extremely low. 22 droppable exotics on ps4, thats a 4.5% chance (if you are guaranteed an exotic, it's even lower when you factor in the chance of an exotic drop), assuming all the exotics are weighted equally, which i highly doubt they are. which is why people seem to be missing the same weapons (suros, gjallarhorn, red death, hard light) so the chances of those weapons dropping is even lower than that. Maybe luck just hasn't been on your side.