Why did Nagato use 6 paths powers only?
In the battle against Hanzo, after Yahiko's suicide, Nagato's inner power awakened, and accidentally summoned Gedo Mazo which instantly impaled its rods inside nagato to get chakra and killed hanzo's men. Then Nagato gets sick, and loose mobility. Then the only long distance power, needed because sickness, is the 6 paths powers.
Source: Nagato