First, Napoleon was at war in Europe. So, he needed money. America paid 60,000,000 francs for the land and cancelled another 18,000,000 franc, which the French owed. So, this was a decent sum of money that the French sorely needed.
Second, Napolean was a pragmatist. He knew that he could not control that huge tract of land from so far away. He was already losing influence in the West. Moreover, he had enough troubles with the war in Europe.
Finally, Napoleon knew that the American wanted the land. Before, American