Try as they might, Microsoft can never meet the code needs of every developer. The world is simply too rich and diversified, full of many niches of functionality. It wouldn't make sense for Microsoft to try and supply libraries to meet all these needs.
Instead, Microsoft focuses on more foundational libraries while its community of developers have taken it upon themselves to write thousands upon thousands of useful libraries and utilities.
Microsoft recognized this and started the NuGet project to make it easier for developers to discover and distribute one another's libraries. A healthy ecosystem of developers who share code and build libraries is good for Microsoft and good for developers.
But then, an interesting thing happened. ...