"that is constrained by a gender role where aesthetic appeal and social interactions are the most valuable assets?"

In theory we should have seen a spike and then slow decline as gender norms and roles continue to become less segregating.

"Yet other categories see linear or token increases."

Yeah, because other categories may manifest their problems differently. Such as young men turning to violence and drugs more than intentional self-harm (almost the inverse of young women). That doesn't mean it's not the problem, just that it's not such a great proof.