Potential explanations:
"Concept creep is the process by which harm-related topics experience semantic expansion to include topics which would not have originally been envisaged to be included under that label. It was first identified by Nick Haslam in 2016, who identified its effects on the concepts of abuse, bullying, trauma, mental disorder, addiction, and prejudice. Others have identified its effects on terms like gaslight and emotional labour. The phenomenon can be related to the concept of hyperbole."
Haslams paper:
https://www.frontiersin.org/articles/10.3389/fsoc.2021.806147/fullAnother factor to it might be the rising notion that being seen as a victim of something can benefit your social status and can be used to leverage social power. In that sense the point would be less about identifying someone as a narcissist and more about being the victim of a narcissist.
"Abstract
Campus activists and others might refer to slights of oneās ethnicity or other cultural characteristics as āmicroaggressions,ā and they might use various forums to publicize them. Here we examine this phenomenon by drawing from Blackās theories of conflict and from cross-cultural studies of conflict and morality. We argue that this behavior resembles other conflict tactics in which the aggrieved actively seek the support of third parties as well as those that focus on oppression. We identify the social conditions associated with each feature, and we discuss how the rise of these conditions has led to large-scale moral change such as the emergence of a victimhood culture that is distinct from the honor cultures and dignity cultures of the past."
Paper:
https://www.researchgate.net/publication/272408166_Microaggression_and_Moral_CulturesAnother factor could simply be that the knowledge is more accessible than it used to be and now people are just using a term that seems to vaguely fit what they experienced because it is easier than trying correctly articulate what and how they experienced. It is used as a shortcut so to speak.