It's like that so you can send your IPv6 packets over 20 year old switches and have them still work. Switches don't care about the IP layer, all they look at is the MAC layer.
Wouldn't it be nice if modern switches could properly route packets without them being framed in legacy protocols? This could be negotiated when you connect to them. But because it's only marginal gain and needs dual-stack switches we just keep the hacks.
Then it'd be a router not a switch and you'd have to replace the router before you can use the new protocol (see: the current IPv6 deployment situation.
This is why layer 2/Ethernet is a valuable abstraction layer not just a "legacy protocol". It allows seamless transition to the new layer 3 abstraction without having to replace all of the hardware everywhere at once.
Here's the thing though: Managed switches are often configured like routers. And even dumb switches have "dynamic route discovery" if we want to call it that.
It would be nice if this could be negotiated away to get a pure IP6 link. If an intermediate link doesn't support that, legacy addressing could still be used. I'm not saying we don't need NDP, just that it would be nice if it could eventually be phased out.
If you're configuring something like a router then it's a router. It may be a crap router but if it routes it's still a router.
> It would be nice if this could be negotiated away to get a pure IP6 link.
Then you'd need WiredIPv6, WirelessIPv6, 4GIPv6, 5GIPv6... layer 2 provides the ability for an abstracted physical layer to transport an abstracted network layer. Remove it and any time the physical layer changes the network layer needs to as well as each of these have unique headers, formats, and data-link capabilities (not all support broadcast for example!).
Every abstraction layer is actively used today, remove it and there is a cost.
