I can see why they wouldn't bother updating them, but why remove them completely? Were they using too many resources or what?
Too much of a pain to test for the OS software developers, probably.
Whenever updating something in the OS, they need to test that nothing else breaks. If they kept the gestures in, they'd have to keep being tested, too. If almost no one's using them, it's not worth the manpower and resources to keep supporting them. This way, UI changes can be made more quickly with fewer resulting bugs.