Refering to something as a cargo cult means that it is repeating the external appearances but ignoring what makes it work. It is a form of magical thinking, that the ritual is what is important. The mental image you should get is someone on a Pacific island after WWII, trying to summon an airplane full of supplies by stamping out a “runway” in the dirt and wearing a “headset” made from coconuts, phonetically reciting landing orders and hoping the planes arrive. The important notion here is not copying but going through the motions and seriously expecting it to work. (See also cargo cult science, Feynman’s popularization of the meme.)
Copying works if you copy the right things. Your cheap knock-off may be missing some features or polish, but there is a market for cheap knock-offs. A taco or t-shirt is still a taco or t-shirt. In gaming, we often politely refer to them as genres, although some are still “Diablo clones.” (MOBAs recently made the transition to genre from “another DotA”.) Other games “borrow” motifs or characters, so we have fads of zombie games, brown “realism,” and a smaller number of snarky, passive-aggressive robots. “WoW with lightsabers” actually sounded like an extremely lucrative idea.
We get into gaming cargo cults when developers or producers have no idea why they are copying things. The market leader has X in the game, so put X in the game. And they seriously expect to make a lot of money, not to make a cheap knock-off. See the infamous keyring. See anytime an executive gives an interview that boils down to “you have to copy WoW to win.” (Those seem to have tapered off.)
Funny thing is, copying can lead to improvement. While there is a first mover advantage, seeing where the first mover tripped can help you get further. (This is where Blizzard has been known to excel.) Maybe the essential feature is not what the original developers thought, and the game works well in spite of, not because of, some core aspect. Are forced downtime, forced grouping, or unrestricted PvP assets or mistakes? We have games gambling on each side of that. Is the economy the heart of the game or an unfortunate distraction? How good is the gameplay when you strip it to its core? The real meta-game is seeing what works in making games.