* Millions of person-hours being poured into a language...
* ...Over a long enough time period that the language can go through several develop-eval-improve cycles - that take real world use cases (And not one-liner bubble sort implementations) into account.
In this sense, it doesn't matter whether or not Haskell was invented in 1890, or 1990. #2 is required for maturity, but so is #1.
(I am not a huge Python fan.)