I recently did a co-operative adventure, and a discussion was started regarding these adventures. The majority of experienced players either rarely do them or do not do them at all. There were a few reasons for this. Many players express how difficult it is to get a group of players together to complete them. However, this was not a problem in the past, before the loot revision in last 2014. At that time, groups were running these adventures on a regular basis. The real reason is closer to the fundamental basis of the game, economics.
The issue with the co-op is that they are simply not economical to run, and thus are relegated to the same category as many of the adventures that accumulate in the star menu and never done. The standard adventures are possible to perform with a single person, even when these adventures can be done with more than one person. Although not intended, most players tend to run them solo, and invite others to get an equal reward for token participation. The experience given to the players proportionally to participation, which the loot table is the same for all players. One look at the required troops and the reward is enough to dissuade players from playing them.
For example, the WhirlWind is rated at a level 7 difficulty, with the estimated total maximum shared cost (at the top level) of 3,314 recruits.
Now, look at Black Knights, which is rated a level 9 difficulty, with the estimated cost of 983 recruits (quick version).
Both set use the same troops, and the numbers shown do not use blocking. Essentially it costs more than 3 times the resources to complete the cooperative adventure, while the amount of reward is only a fraction. Even adding the loot together for all 4 players participating in the co-op, it is just over what one person will receive playing the traditional adventure., and there are three players for this multi-player adventure. Even the building has a much higher cumulative rate for the traditional adventure. The same happens for the event resources: Black Knights gives: 0 / 27 / 67, while Whirlwind gives: 0 / 20 / 50. This gives about the same number of eggs total, at a cost of about 3.5x the number of people.