The Wong-Baker FACES scale traces its roots back to the 1980s, but came into wide use after the Joint Commission, an accrediting agency, named it as one of three possible measures for the assessment of pain.
While the scale itself is useful and continues to be used, the application of it shifted in the early aughts. If you went into your doctor for anything — anything — you might be asked to rate your pain. When patients indicated high pain, a pain medication discussion with their doctor would be initiated.
The scale was one of the more visible elements of the shift in hospitals to assess pain treatment and reward doctors for assigning pain medications. See Improving the Quality of Pain Management Through Measurement and Action