TCP/IP is so entrenched in everything, literally, it will still be in use when we leave this planet and it gets swallowed up by the sun. The news will report the destruction of Earth and explain that it and its inhabitants longest lasting legacy is TCP/IP, then report that the transition to IPv6 is going well and everyone will be on it soon...
The fact that it takes so long to transition to IPv6 and like many other obstruction to technological/social progress are economic and business gain for a certain small group of people and organisations.
The spread and reach of TCP/IP will accelerate at a pace faster than that of the transition to IPv6 indefinitely, therefore we are saddled with IPv4 until the end of time.