Ego, indeed.
The term influencer long precedes social media, the Internet even. Before it were celebrities, columnists, reviewers, authors. And before that public speakers, the term probably goes back at least 19th century.
Roger Ebert didn't need the Internet to be an influential movie reviewer. Same with so many more in their respective niche.
When UGC (User Generated Content), or Web2.0, picked up everyone was considered an "influencer" due to the innate authenticity that came with authentic content. Irrelevant of one had 2 or 200,000 readers. AFAIK influencer was still not a common term.
Next came the came the days of fake social stats, like boosting numbers for the Feedburner widget. 30k Feed sub gave a blog more credibility than only 120 subs.
Not sure when the term exploded and why/who but it was after 2015. What I'm sure of, and also seems to have led to the topic - in itself a perfect example of true influencer ship - is that before its current popularity people earned their badges. They didn't need to call themselves influencer, they had just earned that "reach" over time.
On social media, everyone is a CEO, influencer and whatnot. Just slap it in your profile and party time!
But at least the "influencer" part of that is true... as long as they have an audience of at least 1.
PS: I think the term slowly started gaining popularity post 2016 as the first "self-made" brands appeared (and some disappeared almost as quickly again). I recall that in 2014, while at the digital agency, bloggers were considered a marketing (pitch) component but while internally the term influencer would occasionally be mentioned, influencer marketing was even not a bullet point in pitch decks.
"Time Influencer of the Year" :D
I think it was driven at the height of Instagram and celebrities with 100M followers / then there is the trickle down effect as other ego driven people wanted some glory via association. It is kind of like buying 30 dollar D&G underwear, it is almost the same as a 10K dress.
This is where real influence is derived, influence earned from action.
The drop-shipping nonsense definitely had an effect that made people feel "influential" as they were sent crap in the mail to promote. My niece was getting sent crap through Instagram and thought she was famous ;D