Casey Newton, writing for The Verge:
...two years after it launched, a platform that aspired to build a more stable path forward for journalism appears to be declining in relevance. At the same time that Instant Articles were being designed, Facebook was beginning work on the projects that would ultimately undermine it. Starting in 2015, the company's algorithms began favoring video over other content types, diminishing the reach of Instant Articles in the feed. The following year, Facebook's News Feed deprioritized article links in favor of posts from friends and family. The arrival this month of ephemeral stories on top of the News Feed further de-emphasized the links on which many publishers have come to depend.
I think Instant Articles is good product. However, I've never been comfortable handing over content to Facebook in this manner.
Also, as the article points out, Instant Articles does not seem to fit their long term vision which is heavily based on videos. If Facebook is trying to lure large scale companies to invest in their platform, why not try to go after TV networks and create Facebook TV? This would allow them to go head to with YouTube, Netflix, and all the other players in the video industry.