This is precisely why shipping things in the standard library is a bad idea. It ends up full of cruft that no-one uses because there are better alternatives.
Why? What does that gain?
The standard platform provides Data.Map for maps, Data.Vector for arrays, and Data.Sequence for fast-edit sequences.
It's not even clear what a "built-in" array or map in Haskell would even look like, or what semantics it should have. Especially in a pure functional language, you need to be clearer about what your intentions are. A regular mutable packed array won't work most of the time.
> This is exactly the main problem with Haskell.
> A stunning language with a lousy standard library.