Nice segue into "bragging."
But I think it's also about putting another easy article out there to see how much money they get. Sort of like the "How to Get Rich" ads in magazines of my era. Pay them a little money, and they tell you to an ad in the magazine for "get rich" advice.
I just read of those articles. The successful writer made $800. That means at least 16 Medium reader had to subscribe to pay her off. A defininte zero-sum game.
BTW, I'm from Canada. We have to go through some extra hoops to get paid by Medium. Even then the IRS takes 30% as a withholding tax. Apparently we Canadians can get it back later, but I just imagine the paperwork. I didn't bother signing up.