Over the decades since Rh Immune Globulin became available and a standard for care in 1968, the guiding principle changed from 'looking for reasons not to give', i.e. withholding the injection versus currently 'looking for reasons to give'. Initially, the injection vial was packaged with a crossmatch vial that required a test tube crossmatch with the patient's rbcs. This was a safety step to address the concern of giving such a large volume (at that time I think it was 5ml in the US) of anti-D to an Rh positive individual.
Much later, it was determined that a second injection was required around 28 wks to prevent sensitization of women who might be hyper-responders.
Those safety concerns have been addressed with low volume (0.7ml), low protein formulations. Crossmatching is no longer required.
Performing an antibody screen with a workup is consistent with the original philosophy of 'looking for reasons to withhold the injection'.