The problem is that the overwhelming majority of C#/.NET developers ONLY have used Visual Studio. Monodevelop is not quite up to par, so really, for C#, there's only one choice for an IDE outside of notepad... I used to do more java development, but now do more C#, and I miss the the polish of Eclipse over VS (Incremental Java compiler is a huge win, Refactoring (resharper freeze my machine), Search indexes, Auto completion is still better, code navigation via back button, much better Source control integrations...)