Agile Fails for the following reasons.
1) In reality, most stories/tasks that make it out of the backlog and into sprints are the ones that were inserted by PM's, that support the short term goals placed on the PM. End result, massive technical debt in short order. Even if developers express the 'need' for refactoring, it gets delayed as the PM doesn't get fired for a messy code base, but gets fired for a late deadline.
2) Companies 'turned' to "SCRUM" and imagined/expected that by renaming meetings to "stand-ups" etc.. their productivity would increase significantly. This usually resulted in management blaming their engineering staff for their own follies.
3) Most Biz environments don't lend to a 'perfect' scrum model, as such, many organizations try to 'shoe-horn' practices in situations where it doesn't make sense. For example, an organization may not have the ability to adjust features or timelines, resulting in stories being a convenient way to blame engineers for poor decisions outside of their control (Sales selling products that don't exist and promising it yesterday, or Product demanding features that are unrealistic, etc..).
4) Another buzz word that has little functional value other than to help 'experts' get promotions, who in practice are nothing but glorified PM's with a pinch of snake-oil salesmanship.