Mixing of people from diverse backgrounds happens naturally as a consequence of people trying to achieve their goals through organizations. When we notice that mixing isn't happening, that means that someone is expending energy excluding others and keeping them from achieving their goals.

In some cases it could be the specific background which prevents people from using a specific organization. For example if there is a religion saying that making cars is a sin, then the lack of those people in car factories does not necessarily mean that the car factories are expending energy to keep them out.

Even if "someone" expends the energy, it does not have to be always the obvious suspect.