Different languages make different choices. The disadvantage of Haskell is that if you want to change one value in a collection of a million values that it either makes a full copy or tries to optimize by sharing values behind the scene, both resulting in significant overhead. Most people already understand that pure functional programming languages don’t deliver except in very specific circumstances: Haskell TIOBE rating 0.32%, https://www.tiobe.com/tiobe-index/