Why hasn't Microsoft Exchange changed very much in a decade? As the holder of a lot of really interesting information, you'd think that there would be lots of cool new features they could introduce.
Looking at it from the outside, I think the problem is that they've ended up building a drag racer. They're using the same JET database engine as Access, but heavily customized and tuned to offer great mail handling performance. Just like a drag racer, it's going to be hard to beat its performance going in a straight line, doing what Exchange has always had to do, passing mail between users. The problem is, it's really hard to turn a drag racer. There's a lot of other useful things you could do with all that data, but since the Exchange engine is so specialized for its current requirements, doing anything else is usually both hard to write and slow to run. For example, accessing a few hundred mail messages can take several seconds through MAPI. Doing the same operation on similar mysql data would take a few milliseconds, and requires a lot less code.
They recognize this themselves, the Kodiak project was an aborted attempt to put a modern, flexible database underneath Exchange. I know the bind they're in; there's so many years of optimization in the code associated with the old JET implementation that any switch is bound to mean slower performance initially. I've seen companies wrestle with this dilemma for years; they can't produce a new version that runs more slowly at the tasks customers are currently using it for, but they can't ship the new features they'd like while they're tied to the gnarly legacy engine.