Watch the video. It explains how Destiny actually makes use of operant conditioning to encourage you to buy each DLC and expansion.
If you are unfamiliar with the techniques of operant conditioning, here is a link to explain it in some detail.
http://m.simplypsychology.org/operant-conditioning.html
Edit: Thank you to Bant Spider for the video.
-
This is the case for most MMO's. It's not the operant conditioning we're used to..... this isn't about self pride / enjoyment. This is about having something someone else doesn't have. It's about showing off. We all want every exotic..... Why? So we can say we have every exotic. We don't have a need for over half of them. Maybe Bungie is limiting vault space to keep us from falling too far into this condition. But that's the structure of MMOs..... you have to be better than the person next you. RNG just turns the grind from a million quest solution to a pot luck chance. It's typically the same outcome with a different path.