Haskell doesn't have any more language extensions than other languages of its age, the only difference is that they're explicitly called out.

When Python adds new string formatters or generators or async, they're just in the language. When Haskell does that they require you to explicitly turn the new feature on. It's just a different strategy of managing language change. Versus the classical approach you get a lot more eyes on your language additions and have a nice "beta" period where you can make improvements before there is wide adoption.

This is basically the same approach that Rust is taking but they've been better about removing the feature flag when the feature is stabilized.