The article is about syncing an app that runs locally with other instances of the same app on other machines. Ok. What does that have to do with the title?

> Why haven't local-first apps become popular? (

I think that the title wants to be is "Why haven't more developers written local-first apps for their syncing solution?" because the the answer to title itself is because users don't care. Users (most) want apps that sync between their phone, their tablet, and their laptop/desktop. Up to some point, they don't care how it happens, just that it does and that they don't have to give it a second thought.