ok since this actually falls in my expertise ill break it down for you
first they are not selling out venues.
a girl with 100k followers on instagram "internet famous" cool but she not getting free bottles like that the club unless she know the promoter like that - and that got nothing to do with fame that just comping bottles to good looking girls we'd do that if she had 100 followers.
as far as being "booked" by venues. Ive unfortunately had the mispleasure of booking some "internet famous" people, im talking 500k-1 million followers (now even more). They have no pull. People will like a picture, but they not gonna spend $20 to enter a club to see that person. They bring nothing of value. But someone like Party Next Door(example) with with 700k followers, you can charge $40-50 at the door and 1000 people will still show up and the line be down the block.
someone "internet" famous isnt known to someone like me or the older crowd as well.. Someone with 200k followers aint gonna use that as a bargain chip to get them in the club free. "ay man I got 250k followers let me and 10 people in free"

sounds ridiculous
but if Marlon Wayans has a friend hit the club up and say "ay Marlon + 8 coming through " even someone of that stature (famous but maybe not so much in the spot light anymore) gonna skip the line, get a comp bottle or two and the best VIP table..
internet famous people can get on reality TV, get millions of vine plays but they are all flash in the pans.. here today, gone tomorrow. Very few have made it last long. The original "internet famous" person, Tila Tequila had MULTIPLE shows about her, where she at now ? You got about a year window - at max to turn that "social media fame" into something of substance (flip the money into an actual business). If not, you done out here regardless of how many people still follow you.
ive booked girls in magazines, on billboards, rap videos, 150k followers, 500k followers, 1+ million followers. - no one gives a shyt
Its free -- cost nothing to hit "like" on a picture. Its different to plan your night and spend money at the club because of that girl because she looks good in pictures or because that guy makes popular 6 second vine videos..
edit#2: Also side note, as a nerd myself "who counts pixels" - majority of people with over 15k followers buy likes/followers. I know this because when I pay someone to promo for me and I see them post a flyer and it gets 92 likes in 3 minutes if you click on the people liking the picture its hardly real people. That goes for anything they post.
edit#3: the most ive paid for a "internet famous" model girl to host a party is $500. The sweet spot is around $250-300 (what I usually pay them) because at that price, you break even with 10-15 people coming in with them. Anything near $500 I have to consider the night and what I need for it to be a successful night.
As far as artist goes, the most ive been apart of was $20k - which didnt go through, but based off presales (before being cancelled) looks like we woulda made $40-50k at the door (30k profit) and $70-90k at the bar ($5-8k back profit, horrible bar deal).
Some people worth $300 - some people worth $20k.. end of the day the follower amount might look the same, but they are not equally famous.