Bring the best people to the table
Joshua had been in the presence of God. A theophany had taken place in Joshua 5:15: "The commander of the Lord's army said to Joshua, "Remove the sandals from your feet, for the place where you are standing is holy." And Joshua did so."
Because of his special blessing, he was appointed as one with judicial powers and responsibilities in Joshua 14:6-15. He had a special place. He was courageous as indicated by the spy scenario in Numbers 13:31.
He was most likely the envy of other young leaders. But Moses brought him to the table of leadership because he was the best person for the job. My guess is that he had skills the like of which Moses himself admired, perhaps even envied.