Historically they have treated with independent screws placed into the femoral neck, but this provides no compression to encourage...
Femoral Neck Fracture Surgery
Evolution of Femoral Neck Fracture Surgery

The anatomy of the femora neck makes it very difficult to treat with a plate and screws. There exists a large amount of force that is transmitted through the femoral neck with ambulation, and many of these fractures may also be able to rotate, which would prevent healing in the proper alignment.
For these reasons, stability is important to help these fractures heal. Joint replacement remains an option for older or less active patients, because it does not depend on fracture healing but is not an option for the younger population.