BT needs longer reach. Their finance guys insist they use existing cabinets rather than building to the distribution points closer to the customer. G.fast was designed for 50-200 meters but existing cabinets are often 350 meters away or more. The new standard increases the maximum transmit power up to +8 dBm, with a practical goal of 300 megabits 300 meters. AT&T has been vocal they want a true gigabit to compete with cable, not "up to a gigabit." Comcast is well along deploying gigabit cable to 40M U.S. homes.
The ITU has also started work on G.mgfast (Multi-gigabit.)