When Moses is told that it is time for him to dies, his only response is that someone has to be appointed to lead the people. It is remarkable in that he chose not to recommend anyone to God but accepted the Divine choice.
It is true that Moses had two sons. We don’t know what happened to them. Perhaps they pre-deceased him. It is also true that Joshua had been Moses’s assistant since the first year of the Exodus and he and Caleb were the only two men who would go from Egypt to the Land of Canaan. But that did not mean that either would necessarily have the character to become the leader.
But Joshua is twice referred to as a man of Ruah Spirit, as well as wisdom and strength. He showed he had rational, administrative qualities as well as religious, spiritual ones. This combination is what him uniquely able to carry on Moshe’s work even though no one suggests he reached the same heights that Moses did. Moses responded by laying both hands on as a sign of approval (even though the text has God telling him to place one hand).
Moses and Joshua, like Aaron and Elazar the priests, were chosen by God rather than man. This way of appointing leaders only lasted for only a brief period. Samuel was the last of the great leaders who had a Divine Mandate. From then onward, with occasional notable exceptions the leadership of the Jewish people was neither impressive nor spiritual. Consistently our leadership has failed us.
But we have survived because we are a different, egalitarian, contentious and stiff-necked people. The fact is that these are the very qualities needed to cope even if leadership often lets us down.