system
Given the following post, respond as if you're commenting on Reddit:
human
[1984] Why is the Party so disinterested in Proles?

It is implied that at some point everyone undergoes some kind of intelligence  testing, and that the inner party is nominally those with greatest intelligence,  followed by the outer party and then the Proles, who do not have the intelligence or drive to rebel. 

Is 85% of humanity  really so little a threat that the party sees no need to monitor them at all, but will go to extraordinary lengths to monitor its own members, even to the point of absurd expense? Surely someone intelligent  like Obrien recognized that they were in fact human and a threat to the party.
gpt
Goldstein's book describes it as such (it should be noted that Goldstein's book was almost certainly written by the Party, and so probably reflects the Party's actual beliefs and doctrines too): 

> Throughout recorded time, and probably since the end of the Neolithic Age, there have been three kinds of people in the world, the High, the Middle, and the Low... The aims of these three groups are entirely irreconcilable. The aim of the High is to remain where they are. The aim of the Middle is to change places with the High. The aim of the Low, when they have an aim -- **for it is an abiding characteristic of the Low that they are too much crushed by drudgery to be more than intermittently conscious of anything outside their daily lives** -- is to abolish all distinctions and create a society in which all men shall be equal. Thus throughout history a struggle which is the same in its main outlines recurs over and over again. For long periods the High seem to be securely in power, but sooner or later there always comes a moment when they lose either their belief in themselves, or their capacity to govern efficiently or both. **They are then overthrown by the Middle, who enlist the Low on their side by pretending to them that they are fighting for liberty and justice. As soon as they have reached their objective, the Middle thrust the Low back into their old position of servitude, and themselves become the High.** Presently a new Middle group splits off from one of the other groups, or from both of them, and the struggle begins over again. Of the three groups, only the Low are never even temporarily successful in achieving their aims. It would be an exaggeration to say that throughout history there has been no progress of a material kind. Even today, in a period of decline, the average human being is physically better off than he was a few centuries ago. But no advance in wealth, no softening of manners, no reform or revolution has ever brought human equality a millimeter nearer. From the point of view of the Low, no historic change has ever meant much more than a change in the name of their masters.  

(emphasis mine)  

Basically, the Party has looked at political upheavals throughout history, and realized that the lowest echelons of society do not rise up without a middle class leading them and giving them directions.  Therefore the Low, when left alone, are simply no threat, because they will not rise up by themselves.  Simply surviving day to day is enough of a struggle for them, and they do not have the extra energy to cause organized trouble unless there are members of the middle class guiding them.  So the Party leaves the proles alone, but clamps down *hard* on the members of the Outer Party (ie, Winston's social class) because they're the "Middle" in this equation, ie the ones who can actually inspire the proles to cause trouble.