People were still finding bugs in common implementations of timsort as of 3 years ago. It's not unreasonable to stick with a somewhat more conservative choice for a core library function until there's more reason to have confidence in the implementations of timsort.
Didn't one of the most simple algorithms, binary search, suffered of a bug in a standard library (was it Java?) a few years ago? If IIRC it was a corner case, I should check it because I don't recall the details, but it looked robust code.
If I recall correctly, the bug only applied for arrays/lists of length greater than 2 to the more-than-astronomical. Not something that anyone ever encountered in the wild, because current hardware doesn't have enough memory.
Edit: The article linked in the other comment says the Java dev team didn't even bother to implement the "proper" fix, but merely adjusted how much space is allocated.
