There are just things you can’t do without having generics in your language. User-defined collections, for one. Statically typed higher order functions, for another. To paraphrase (I believe) Bob Harper, you either have a statically typed language with generics, or you have a dynamically typed language. That’s the result of not having generics. Code that needs them becomes more dangerous and error-prone.
I like to liken it to house construction. Imagine if a number of people demanded that natural gas and water be combined. Why do I have to make two separate pipes? They even look the same!