why should you not take ferrous sulfate with eggs,grains,dairy,coffee or tea?

If you take eggs, grains ,dairy, coffee or tea at the same time as taking ferrous sulfate it becomes harder for your body to absorb the iron. It is best to take the ferrous sulfate ,one hour before ,or two hours after, these food.

Certain foods can make it harder for your body to absorb ferrous sulfate. Avoid taking this medication within 1 hour before or 2 hours after eating fish, meat, liver, and whole grain or fortified breads or cereals.

see https://www.drugs.com/ferrous_sulfate.html