謎ですね

Data.Map.Strict
https://hackage.haskell.org/package/containers-0.5.9.1/docs/Data-Map-Strict.html
> The implementation of Map is based on size balanced binary trees (or trees of bounded balance)

Data.HashMap.Strict
https://hackage.haskell.org/package/unordered-containers-0.2.7.1/docs/Data-HashMap-Strict.html
> The implementation is based on hash array mapped tries. A HashMap is often faster than other tree-based set types, especially when key comparison is expensive, as in the case of strings.