I'm not so sure it's actively seeking homogenized outcomes so much as prioritizing getting (most) students through at some fairly unambitious level over doing the most they can for top achievers even if that means lots of others get left behind.
There is incentive to push pupils up the bell curve to the mean, and incentive to push (the big heavy) bulk of the curve to the right, but much less incentive to push them down the other side.
I'm not so sure it's actively seeking homogenized outcomes so much as prioritizing getting (most) students through at some fairly unambitious level over doing the most they can for top achievers even if that means lots of others get left behind.