Earlier quoted context omitted.
Lack of well-made strings puts the language as a whole in a bad light: if you don't bother supporting fundamental practical needs, asking me to use your experimental, half-engineered proof of concept is arrogant.
There are well-made string types for Haskell! People are just understandably confused that there are so many of them.
But the problem is that strings must be a built-in feature in any programming language that wants to be taken seriously (with an exemption for specialized ones that don't need strings, like GLSL). What would you think of a hotel that doesn't have mattresses but allows guests to bring their own?