There are a lot theories related to the use of IoC .NET. I think there are a fair amount of developers that don't have the experience in the area. They didn't come from a Java background. They came from a classic ASP, and a VB6 background. Also, Microsoft didn't really promote the use of IoC up until recently.
Further, using IoC assumes several things. First, you must understand what it's used for and what you're getting out of it. Secondly, you must develop your code so that an IoC container can actually be used.
IoC is more than just using another item in the toolbox. It's about knowing how to use, knowing when to use it and maturing as a developer.
As it relates to .NET, I've several IoC containers. I've used Windsor, StructureMap, Unity and, most recently, Ninject. Keep in mind, though, I haven't used all of them in real applications. I like to play around and see what's going on out there. I've found that the market for IoC containers .NET is quite good.