Bungie learned about Destiny's notorious loot cave before launch but didn't shut it down until several weeks later. At a GDC panel, the development team revealed why they waited so long.
The so-called loot cave was a cavern in Destiny where enemies would quickly spawn over and over. Players would gather there to mow down these enemies and collect the flood of loot that they dropped. While Bungie noticed this behavior early on, they didn't put a stop to it because it wasn't hurting the game's balance. Bungie's John Hopson said that farming the loot cave wasn't nearly as profitable as players believe.
"They were very weak enemies that didn't drop very good loot," Hopson said (via Kotaku). "The funny thing is that we knew about [the loot cave] before launch, we knew that this was potentially exploitable activity, but we didn't care. The actual drop rate per minute spent is not any different than anything else."
Hopson believes players kept shooting away at the loot cave because it required less effort than other activities. It's a way to earn loot while barely paying attention to the game. Bungie was apparently okay with this.
The turning point, Hopson said, was the sheer amount of complaints that the loot cave generated. Players would report the folks using the loot cave as cheaters. The players that tried to disrupt this farming would then get reported for misbehavior by the loot cave users.
"The time of the loot cave was the highest peak of players reporting each other for cheating."
Bungie effectively killed the loot cave by upping the respawn timer on the enemies in that location. At the time, they said it was because this farming wasn't how the game was supposed to be played.
"Shooting at a black hole for hours on end isn't our dream for how Destiny is played," Bungie said at the time. "Our hope is that social engagement in public spaces is only one part of the Destiny experience."
Players have since found other spots in the game where they can quickly farm loot. For example, some players like heading to the Skywatch to kill endlessly respawning Hive Thralls.
While this mindless farming isn't as fun as the normal activities in Destiny and maybe not as rewarding, it's a lot easier. That's enough to get people to keep doing it. This behavior isn't unique to Destiny. If you have a game based around progression or loot, players are going to find ways to half-ass their way through it. That's why you'll often find AFK players in World of Warcraft PvP battles or Heroes of the Storm matches. People want the rewards for playing even when they're not really playing.
All the developers can do is find ways to make this sleep-grinding as difficult as possible and make sure that the incentives for active participation are far more compelling. They need to make it clear to players that these low-effort activities are a waste of time, too. For example, I wish Bungie had told players the rewards per minute ratio for the loot cave was worse than other activities back in September. That sort of data would've been a lot more convincing than telling players, "Hey, you should socialize more!"