REST has "failed" in the same way that many original visions of the web/APIs/protocols have "failed" - you have a few "no-true-Scotsman" purists complaining about differences in implementation; meanwhile a great many real-world developers are quite happy and productive in a REST-like paradigm and don't particularly care that their API doesn't fit some Platonic ideal.

Could things be better? No doubt. But REST (or something like it) is largely "the way things are built" these days and most people don't mind. Calling it a failure is quite a stretch IMO.