Cisco's Packet Tracer is a training simulation, and as such, often does not have features found on real Cisco platforms, even those represented in the software.
As to why Cisco does not simulate all the features, you would need to ask them, but I would guess they figure the effort involved is not worth the investment for what they expect to use this software for in training.
That said, I would expect to see additional IPv6 features provided in later versions.
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