The Proles need a leader to take them to revolution. There is no such leader, and the Proles are basically happy in their ignorance. They are kept poor and dependent on the Party, but independent of Party events and surface control. While it appears the Proles have more independence and freedom than outer Party members, the Proles are perhaps even more controlled by unseen forces, lack of knowledge/education to overthrow the Party, and no real way to organize their numbers.
Winston sees only the freedom they have to move around, sing while doing laundry, and live without worrying about thought police. He does not recognize the depth of the control the Party has over the Proles by keeping them in destitute poverty.
At first Winston believes that if there is hope at all in a revolution that it must lie within the Proles because they are removed from the Party and it poses less of a risk because they have not been indoctrinated with their beliefs and brainwashing. Winston, after seeing the Proles more closely, realizes that while they are his only hope, they will never revolt. They have no drive or ambition to do so and they have no need to revolt since they are not a part of the Party. He realizes that they are mostly content being independent of the Party. They possess a happiness and peace that he cannot attain. They also lack the knowledge needed to overcome something as big as the Party and Big Brother. He realizes a feat this enormous can only be accomplished by Party members themselves and with vehicles like the Thought police and the brainwashing he can never expect to see a successful revolt in his lifetime. With Newspeak advances at the rate it is and diminishing expression he realizes that it may never be possible.
Economic restraints and violence have long been used by totalitarian governments. These techniques work in the short, but have historically proven to encourage the revolt of the common people. In Orwell's society, however, he has added the Thought Police. By learning to control the thoughts of the people through language and torture, the Party ensures their power. The Party is able to change the beliefs of the people by changing the way they think abou things - this is the principle of Newspeak. In addition, as happened to Winston, when a person demonstrates rebellion, the Party is able to tap into their deepest fears and then uses those fears to gain allegiance. The Party will not execute anyone until that person has been converted. Therefore, no rebel is a martyr to the cause, but instead a willing victim. Willing victims do not rebel.