I see an analogy between what happened to Agile and what happened to "Object-oriented". Both were, at a time (IMHO) genuinely useful, fresh and thus popular with developers.

Both got a bit overdone (Java: everything must be a method of an object!) and hijacked by the Certified Formal Methodologies people and pointy-haired bosses. People found the limitations of both Agile and Object-oriented - there's no silver bullet after all. The good things got incorporated into the set of good practices (and became obvious and thus not worth mentioning) the bad things are labeled as bad (although some stick with us.) Life goes on.

Agile is obviously a bit earlier in this lifecycle - I believe there are no mainstream object-oriented conferences anymore while Agile ones still exist.