I'm more inclined to the idea that social media attracts and congregates narcissists. The platform is ideal for photo and video sharing, which attracts a certain type of narcissists, the type who exhibit their person and personality through these media, namely photos and videos.

There are other narcissists (if we can define narcissists as people with a desire to seek attention) who don't do so via photos or videos but via other means. For example, people who are extremely good at making money might show off a new Ferrari, probably not via taking a photo of it and posting it but by driving it through the streets and showing off. Or people who are extremely good at doing research might show off a new finding not by making a post somewhere where 99% of the population won't understand anyway, but by publishing in scientific papers and then plastering copies of them, likely with their name highlighted, in their office. Such other forms of narcissism is no less narcissistic than those who show off their summer bodies on instagram. They just don't find social media an adequate platform for their showing off needs.