It may well be done by cargo cult, because there's a lot of catchphrases to do with Agile that people are eager to use. I can definitely see how people can get excited, do a superficial attempt at implementing, and then wonder why it didn't work.

But IMO the main thing about Agile is short feedback cycles. If your feedback is real (not just pleasing management), you can't avoid improving your product faster than some methodology (I hesitate to use such a word; it's really just rules of thumb) that insists on taking a long time between feedbacks.

This also means that it's somewhat tautological that Agile methods will work. If you keep making product, you're getting work done. If you're not getting work done, you're not doing Agile.