The number of keys you have determines how many times you can get loot from running Prison of Elders. You only get 1 key per level per character per week for beating it. If you have 20 keys (which some people do) then you can run it 20 additional times for loot that week. If all you have 0 keys and all you get is the 1 from beating PoE the first time, that's the only time you can get loot from that level that week. So for those who want to run it more, yes, they have to farm to get the keys. Is it a requirement to enjoy the game? No. Are they being forced to farm? No. If farming is ruining the enjoyment of the game, then don't do it.