Interesting video. I have a couple of friends who played Destiny religiously since launch and could never understand what kept them going. From an outside perspective it kind of does look like a gambling addiction.
People who have a lot of time put into the game probably don't. Using myself as an example I really want a certain pair of rare hunter boots that can only be received randomly through 2 activities in the entire game. Leaving me with a possible 6 attempts to pull the lever on that slot machine. Of the attempts pull the lever maybe twice, and only if a friend asks me to help them with the activity. I WANT THOSE BOOTS, but I know even if I sought to pull that lever 6 times a week I likely wouldn't get it and choose to do something that I enjoy doing.
What keeps me going back? Stellar gun play that isn't a rehashed CoD or Halo with a massive active community. The option of going into PvP with tons of ways to set up my characters and play differently completely on a whim and even right in the middle of a match. A huge variety of available guns and gun perks. There is of course a meta to that, but welcome to FPS PvP, there always is a meta for it. If I'm not feeling like PvP I can get some friends together for a bit of PvE content and chat while pwning Mobs in a variety of ways.
I mean, if you enjoy the FPS gamestyle and have not run the Vault of Glass I pity the foo. There is literally nothing I could possibly want from that raid, but I keep doing it without batting an eyelash.
To top all that off, the community isn't at the point of going sour. Ignore the forums on Bungie.net they are always sour. Even the /r/ is getting to the whine and complain stage. The people you actually meet through the game aren't toxic at all and are still unbelievably helpful. Something that left other FPS powerhouses a looong time ago.