The quote about the stdlib being "where packages go to die" was, for a long time, considered a feature and not a bug. The theory was that once a package is in the stdlib its development should slow to prioritize stability over new features.

This may somewhat explain why lots of successful packages are not in the stdlib: putting them in effectively killed future development until a few years ago. But today that argument is inconsistently applied and I'm not sure if it's a rule worth keeping.