The difference, of course, is that lebron James and Tom Hanks have some other talent that can explain their fame, and The Atlantic journalists also are influential because of some other thing they do (besides influencing). These Instagram people are influencers because... why? What underlying talent or past event launched them into their positions?

Reasons for fame, while interesting in themselves, only matter insofar as they determine the demographics of a celebrities following and how likely that demographic is to try the products they associate themselves with.

A small thought experiment now, say I run a restaurant and both Tom Hanks and Lebron James go on national television and declare it their favorite place to eat, what happens? I'd say starting the next day I'm going to be flooded with reservations despite the fact that the talents that make them famous have nothing to do with their ability to judge food.

Influencers are influencers because a large group of people act collectively to give them influence. The reasons why people give influencers such influence is varied but as a business owner all that really matters is how much that influence may be worth monetarily.

George Clooney has no qualifications as a barista or in coffee at all, yet Nescafe still use him to shill off their terrible, polluting coffee machines.

Why should I trust him on coffee machines any more than some hot girl in a bikini on Instagram?

I think influencers are similar to Linkedin type thought leaders. Every time I log in there a new one pops out in my feed. Some are collecting awards from a thought leading organization which no one had heard of, while quoting some fake Sun Tzu proverb.

I think they are doing pretty well for themselves but they never seem to have anything interesting and original to say.