When confronted with intense accusations of rebellion and idolatry by a delegation led by Phinehas the priest, the eastern tribes make a highly calculated choice in their defense. Although Phinehas spearheaded the rebuke and spoke on behalf of God, the tribes choose not to address him directly. Instead, they direct their response entirely to the leaders of the Israelites.
The primary approach among commentators is that the tribes realized they had no need to justify themselves to God, whom Phinehas represented. God sees into the depths of the heart and already knew that their intentions in building the altar were entirely pure. He knew it was never meant for idolatry or for offering sacrifices outside the Tabernacle, but simply to stand as a lasting witness for future generations. The Israelites, however, cannot read minds or see hidden motives. Therefore, the eastern tribes had to direct their defense specifically to the national leaders in order to prove the truth and clarify their true intentions [אברבנאל, אלשיך].
Building on this, another perspective suggests a strategic logic in their choice of audience. The tribes understood that if they could successfully clear themselves of the earthly charges of creating division and betraying the nation of Israel, the much heavier accusation of rebelling against God would automatically fall away. By proving their loyalty directly to the leaders of the people, they would naturally clear their name before God's messenger as well [מלבי"ם].