When meiosis occurs in females, why is the cytoplasm not divided equally in the four resulting cells?

Answer 1

The three other polar bodies are basically discarded. The egg retains most of the cell cytoplasm to increase the size. When fertilization occurs, the egg will undergo rapid cell divisions into a cluster of cells. Before the blastocyst implants, it remains roughly the same size as the original egg. However it now has many, many smaller cells. The volume of cytoplasm from the original egg is needed to support this much cell division and the formation of the blastocyst cavity before it can implant itself in the mother's uterus. It is only after the blastocyst implants and breaks out that the embryo can starts to grow in size. Prior to that, the cells are multiplying by using cell material that was already there in the original egg. That's why the egg has to be large to start with.

Answer 2

Because the other cells are "polar bodies". They do not contain all the genetic material necesary for the egg.