I believe there are several reasons why IPv4 refuses to die and why people are hesistant to change to IPv6.
1) Most (older) software/games are either not compatible with IPv6 or still expects an IPv4 address to work.
2) Easier for remember/type a non-DNS/hostname-based adresses. I think the average person is more likely to remember a 192.168.X.X address than the IPv6 equivalent.
3) Familiarity and customer expectations, people expects their software to use IPv4 addesses because that's how it's always been.
The hardware/software companies knows this and thus uses IPv4 by default.
4) Lack of backward compatibility in general as previously mentioned in the comments.
Biting the hand that feeds IT
