Mike Stall explains the complexity of the VS suite:

Visual Studio is over 43 million lines of code, there are over 30 teams working on different pieces, with roughly 700 developers checking-in code to 11 different virtual build labs that are then integrated on a rotating schedule producing over 100 different builds of the product daily. In addition we have interdependencies with SQL and MSDN.

No need to wonder why it's late - that many developers is a solid sign of an ongoing death march, complete with the attendant tight coupling to other systems that they don't fully control. That's got to be a complete horror show to have to work on...