I don't think that's the point at all. If anything it's "some Microsoft frameworks are too big and complicated" (but others - F# - aren't so let's try those)
F# is just another CLR language, so the "Framework" is just as big under F# as it is under C#. It's just a different way of looking at development (specifically, the OCaml way).
.NET is big because it actually contains a lot of useful APIs. I think this is a natural outgrowth of a framework that attempts to be all things to all people.
I'm not a .NET apologist, but I use it every day at work and it has it's strengths and weaknesses (like everything), but overall it is a fairly well-designed framework. My biggest beef with most .NET development is that you have to do it on Windows...
