If a woman has a breast removed, with todays technology, why can't an artificial breasts be used in its place?

Reconstruction. Most breast removal is for cancer treatment. Reconstruction is designed to replace the tissue with a match for the normal breast. This involves implants and sometimes tissue/fat transfer. There is not such thing as an artificial breast, and such an item would lack sensation. As diagnosis and treatment of cancer improves, breast sparing is more commonly used.