So the article goes on to mention a few individual features of the language which are good features and would definitely be appreciated by those that have already seriously committed to learning and using it, but are pretty opaque to an outsider.

The real killer feature of Haskell is that it is the closest language to mathematics and makes reasoning mathematically much easier than even other functional languages.

Superficially, the syntax has more similarity to mathematical definitions and statements, the conventions (like single letter variables) are borrowed from mathematics and don't feel ugly or forced. Lack of side effects, composition, currying etc and other functional benefits much more neatly line up with how functions are treated in maths.

Ultimately it's still a programming language, and is used much more for traditional engineering or compsci applications than something like Maple or Mathematica would be in Mathematics research, but nonetheless the main draw of Haskell is that it will feel like a home away from home for mathematicians and not because of 5 features noted in this article.