It really sounds like a "not true Scotsman" argument, but I've had Agile fail when the team failed to use Agile. As I wrote above, points inevitably became a proxy for time in one manner or another. Production was pinned to a certain number of points (say 15 per developer per sprint).

I can't throw it all on management either. People who should know better will accept 2 days worth of points for conducting training or attending a workshop.

Largely, though, I would say it's a simple matter of not understanding how Agile works at all. It has just become, "you score points for doing stuff" (in proportion to time, but it's not time, but it is).