Why doesn't Windows Update uninstall obsolete updates?

For instance, if you install IE11 on Windows 7 you don't need any of the updates for IE8/9/10 anymore. Yet short of manually going into Programs and Features > View installed updates and plucking them yourself, there's no (automated) way to remove them.

It's possible the user could uninstall IE11 and go back to whatever the old version of IE was, but it's also possible to reinstall the relevant updates again. Given the way CBS works, the more updates you have the longer it takes to check for updates so you'd think the benefits of making each and every update check faster would far outweigh the one time inconvenience of having to reinstall updates in the (rather unlikely) event the user decides to uninstall/revert...

 

The first time I check for updates, I find a lot of IE 8 related updates, I deselect them all and after installing IE9 for instance, I then need to check for updates again and what I notice is all those IE8 specific updates no longer show up.

 

They do.
Updates through Windows Updates by default downloads their uninstaller as well
Manually Installed Updates usually don't, which tends to mess up the Windows Update ... ie Update fails cause it couldn't remove an older offending update.

If it didn't get automatically removed, it think that someone is using it still.

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Just not for IE, for legacy reasons and it's part of the core OS.
You have to manually remove them.

By default, Windows 7 comes with IE8.

I worked on older software that have "helps/documentation" try to call on older IE8 stuff and crash cause I only have IE11 with all IE8 references removed.