Why did Sitting Bull and his men surrender?

Sitting Bull was known among the Sioux Indians as a warrior, but by the late 1870s his leadership was a spiritual one, and he influenced many leaders among his peers, such as Crazy Horse and other military leaders in the tribes which respected and followed him. On or about 1877 he fled into Canada but returned to the U.S. with his people starving in 1881 which is when he and his men surrendered. After serving a two-year term as a prisoner of war, he was allowed back into the Standing Rock reservation between North and South Dakota, where he was freed.Sitting Bull and his men did not surrender to the U.S. in 1876 because they were defeated. The military leaders in his company were, in fact, victorious against their American counterparts in the Battle of Little Big Horn in 1876, but Sitting Bull and his men had decided to flee into Canada after this battle to find a safe haven. Sitting Bull's company had already disbanded into smaller groups to avoid retaliation from the US Army after the victory at Little Big Horn. Sitting Bull and what was left of his group spent one year trying to hunt buffalo in their native Montana and fight off skirmishes with army men, before seeking refuge in Canada, a year later, in 1877.What ultimately led to Sitting Bull's return back south was the fact that the buffalo he hunted were disappearing, and U.S. Emissaries were successful in persuading many of his group members to return to the U.S. reservations with promises of riches there. Given the pressure of northern Indians as well, the temptation to return to the U.S. caused Sitting Bull and a group of sick and elderly Indians to return back to the U.S. and surrender in 1881. Ultimately, he was killed by Indian police after he resisted arrest for participating in a Ghost Dance uprising.
https://www.history.com/this-day-in-history/sitting-bull-leads-his-people-into-canada