why weren't the proles indoctrinated with the ideology of the party?

The Proles represent 85% of the population. The proles are considered mindless animals by the Outer Party. The Inner Party is not concerned with them as long as they wallow in their own ignorance. The Inner Party controls them by feeding them things like porn, the lottery, and cheap alcohol. As long as the proles are wrapped up in their small lives with their primal needs met, they won't question politics.