Stereotypes are reductionists views of the world.
Its part of the brain system of integrating information, simplify, simplify, simplify and integrate to existing patterns.
This makes learning easier, imagine the brain had to track every variation seperately, but also glosses over those variations because they don't fit the previously reinforced patterns.
So, stereotypes are not just a big conspiracy, they're actually part of the way we see the world.
The less information you have, especially if its not first hand information (the media for example), the more distorted the view, the coarser the stereotypes will be and the farther away a random individual you meet will correspond to it.
With education, the classification system becomes finer, its still stereotypes, but so close to the actual person's individuality that its actually meaningfull instead of being alienating.