Moshe davens for the forgiveness of the Jewish people after the incident with the spies. This is very similar when he prayed for forgiveness after the sin of the golden calf. With both, Moshe beseeches Gd on the Jews’ behalf telling Gd to forgive them for His sake, lest the nations of the world have the wrong impression of Gd. With the sin of the golden calf he prays saying to forgive the Jews in the merit of their forefathers. Here, with the sin of the spies, he doesn’t use this tactic and instead he falls on his face begging for Gd’s mercy and compassion. The facet of for Gd’s sake is used in all cases, because we want the world to know Gd because of what He does for us.