This is kind of a meta-story, or even advertisement (although very good advertisement). Publishing it in-between their usual content would raise a few ethical questions.

It'd also be a bit useless to tell readers of the Economist how great they are, and, as long as they can't get it printed in the NYT or similar, Medium probably is the best place to reach their potential market.

"It’s a place for our engaged, smart Medium audience to interact with our journalists, get involved with news gathering and research, browse a carefully curated blend of original and archive pieces, and get a glimpse of the unsung work that goes into The Economist."

They've also been experimenting with Snapchat. So they're definitely open to pushing their content out through alternative channels.