Final answer:
Alcatraz was closed down because the prison was no longer needed. Native American activists who had occupied the island began to leave on their own and were eventually removed by the government.
Step-by-step explanation:
Alcatraz was ultimately closed down because the prison was no longer needed. The government negotiated with the Native American activists who had occupied the island, and they began to leave of their own accord. The final holdouts were removed by the government in June 1971, and the occupation of Alcatraz brought national attention to the concerns of Native American activists.