Sorry, but that is a nonsense excuse.
The (now abandoned) Spring.NET project[1] was started in 2004, not too long after (Java) Spring started.
It's easy to criticize Java Spring, but it's a good example of a long-lived successful Open Source project. It's also easy to argue that Spring isn't as useful in .NET as in Java.
But I can pull up many, may other examples (the .NET Lucene port etc).
My point is that the .NET OSS ecosystem is NOT a new thing, but it keeps getting killed off. The typical example is that a .NET project starts to solve a problem, gets it 30-40% solved, then Microsoft releases a project that solves a different 30-40% but sucks all the oxygen out of the ecosystem.