Pure FP languages are still pretty niche, but what has happened is the big mainstream languages like C# and Java has adopted more functional features like highe

Pure FP languages are still pretty niche, but what has happened is the big mainstream languages like C# and Java has adopted more functional features like higher order functions, lambda syntax, increased focus on immutability and so on. So functional languages are clearly trendy among the language designers, from where the inspiration trickle down to the mainstream.