Why was there no successor to the chair of Moses after Joshua?

After Moses and Joshua came the period of the judges, lasting about four hundred years, and these judges were the ones with the wisdom. Just as Moses had, the judges had access to the Urim and Thummim, later called the ephod, by which you could get direct yes-or-no answers from God, provided you framed your question that way, so they were privy to divine information as well as being the practical judges of the people. When the period of the judges ended and Israel had kings like Saul, David, and Solomon, the prophets took over that role, determining whether someone had sinned and receiving revelation from God, and there were schools of the prophets during this time. In the king's court there was also the master of the palace, like a chief of staff, who levied judgments on lesser matters while the king handled only major issues like war. Remember too that when Moses asked for help, God gave him seventy elders with the same spirit of Moses. So there were always leaders to do this, and the precedent for it was set by Moses himself; the line of God-appointed judges and prophets continued.