> How so? It was adopted by every country in the world except for 3.
Adoption is hardly a measure of success, given that the adoption is only widespread because of imperial colonization by a couple of nations which happened to use it.
None of the science disciplines on Earth use imperial, and besides some manufacturing in the US or companies forced to use those products virtually no engineering disciplines use it either.
You're not parsing it correctly. The OP was clearly using "failing" as a noun (synonymous to "weakness" or "flaw"), not as an adjective (something that's in the process of becoming a failure).
How so? It was adopted by every country in the world except for 3.