UX issue, and UX issues are often downplayed by engineers, leading to adoption failures.
Another such example is SELinux, which would have prevented so many vulnerabilities from being exploited, but whose poor UX also caused everyone to disable it at install time.
SELinux's UX was significantly improved many years later, but already too late to change ingrained opinions. There are a lot of ingrained opinions about IPv6 too.
> SELinux's UX was significantly improved many years later
in what way?
Conversely it means people who have ISPs that do IPv6 just have IPv6 and don't need to turn it off. Because it just works. The other day my IPv4 was down and I didn't even notice.