I've been of the opinion this is one of those "the art advances one funeral at a time." A lot of people are married to IPv4 and its arcane warts and really, really do not want to deal with IPv6 even though most of the core concepts are almost exactly the same thing, except better. I can't imagine anyone who dealt with V4 multicast ever wanting to go back, and I bet they've memory-holed parts of V4 that simply can't be used anymore and so have been turned off for decades(RIP to RIP). Has anyone seen the automated address assignment in V4 ever work? The usual hint it even exists is that if you see one of those addresses it means something is messed up in your Windows host or the DHCP server died.

People complain about dual stacks and all that but with a modicum of planning it is minimal extra effort. Anything made in the last decade has V4/V6 support and unless you're messing with low level network code, it's often difficult to even know which way you're being routed. Network devices pretty much all support using groups of names or addresses and not hard coded dotted-quad config statements now, and have for a while. And that was good practice on V4 networks too.

Part of it is probably that remembering various V4 magic is easy enough to do but feels complicated enough to be an accomplishment. In V6, there is no point in doing most of that because the protocol has so much more automation of addressing schemes. But if you like those addressing schemes, V6 can do them even better. You can do all sorts of crazy address translation on either the network or host id portion, like giving an internal network a ULA that is magically translated to a public network prefix without any stateful tracking unless that is desirable.

I feel there is some analog to DNS in that regard, people who have gotten used to DNS don't give a damn about host IP addresses but some people seem to really like the idea of a fixed address statement. People also seem to be stuck on the idea that NAT creates some kind of security when that's really the stateful tracking that is required for many-to-few translations (thus making firewalls a common place to implement it), not the translation itself. Similar to certificates/pki versus shared keys, yes, one is more upfront effort but that's because it's solving the problem of the Sisyphean task that is the other.

edit: This all reminded me that we lived with dual stacks before, in the IP and IPX days, or DECnet, and that GE Ether-whatever, and those had less in common. IPX mostly died with Netware but it had a number of advantages that wouldn't be bolted on top of IP for years, some of which are present in IPv6. I rather liked IPX and had history gone differently that it used 48-bit addressing would be causing us to discuss whether or not EUID was a mistake or not :)

IPv4 link local addressing is awesome for direct PC to PC connectivity with no hassle