I hear this question fairly often... usually in regards to a product that depends on another (that just shipped). For example, "Why is it that Data Protection Manager cannot do an item level restore on a SharePoint 2007 Document Library?!?!?". Well... SharePoint just shipped, and now the DPM team is hard at work to add that feature. No one has answered this question better than Raymond Chen:
The answer to "Why doesn't this feature exist?" is usually "By default features don't exist. Somebody has to implement them."
It's not like every feature you can think of comes out of your brain fully tested and implemented, and then some PM somewhere files a bug to have your feature removed. Features start out nonexistent and somebody has to make them happen.