They could also improve the language. Map, filter, and reduce are such fundamental concepts.
It's pretty trivial to write your own custom map/filter/reduce though.
But oh man it's the same discussion every time when Go comes up here
Same with map, they are a constrained for each that is guaranteed to be a correct implementation.
Edit: Also, for loops are just a way of implementing a mapping, where you have data A that you want transformed into data A*. The map is the fundamental concept here, not the for loop.
In fact in many languages much of filter() can be implemented in the for construct rather than its body.
The map/filter is more fundamental in a mathematical sense. If you turn a list of A turned into a list of A*, the 'mapping' is the fundamental concept, the 'for' loop is just an implementation detail. Maybe the computer did it in parallel, or in random order, or I asked you to turn a pile of towels into a folded stack of towels. The same way if I say 'want to watch a movie' - the movie the fundamental concept, whether it's digital, film, etc. is irrelevant.
And maybe that is part of the problem with a generic 'map' your not really sure the underlying implementation, is it parallel, clustered, serial, etc? So you end up with map(), parallel_map(), mpi_map(), etc, and how to you control the parallelism. Do you just let it default or do you have levers to control the batch & interleave. Pretty soon, its not such a simple construct anymore.