There was no way to make the transition to IPv6 without dual stack. The problem was much more that the precise dual-stack approach was not well thought out, when it should have been a fundamental part of the IPv6 RFC itself.
Any ISP who wishes to move to IPv6 still to this day has to consider how it will handle clients that don't speak IPv6, servers that don't speak IPv6, routers they own that don't speak IPv6, and peers who don't speak IPv6. There is no way to make all of this work without having devices that translate between the two (losing most of the benefits of IPv6 when going through this translation, of course).
When you've spent 10 million dollars or more on a router that doesn't speak IPv6, you don't change it one year later just because a new protocol has come up. That thing is there to stay for 5-10 years, and you just work around it as best you can.
