[lenkite]

Because C#, at several points in its history, sensibly took the decision to explicitly break backward compatibility to satisfy legitimate requirements, adapting and evolving to the tenets of modern software practices. (Generics and new collections)

Whereas due to C++'s "never break compatibility" decision, the standard library has progressively decayed over time. It has become a bloated, rotting dinosaur where even the slowest of interpreted languages can comfortably beat several of its aspects. (Ex: std::regex is pathetic and pitiful, vector<bool> triggers laughter, substandard maps, etc). Considering that C++ thumps its chest and loudly proclaims its superb performance, this has now become a sad joke.

In the natural world, a species that cannot adapt to new circumstances and never discards undesirable characteristics simply perishes.

The C++ Standard Committee has firmly and unequivocally decided that the C++ language should mirror the same approach and limp down the road, carrying the full-weight of its sins for all its journey, until it falls into oblivion.

[pjmlp]

Note that as documented in the history of F# HOPL paper, .NET already had a generics prototype before 1.0 release, Microsoft decided to go ahead without generics to avoid delaying it further until they were stable.

Also breaking everything a couple of times is why most corporations are nowadays stuck in a Python 2 / 3 parallel world in .NET Framework / .NET Core , or in Xamarin.Forms / MAUI, UWP / WinUI,...