My impression of it is that it's an "API" that's masquerading as a dumb relay, essentially giving almost datastore-level access to the frontend client (even though they don't market it that way). And this is done so that "Frontend devs" can just do "Frontend" things with access to all the data they might end up using. A bit snarky, but I do see it as a way to just "offload" the problem down the line, instead of thinking about the API-usage and what it means for potential frontend clients. That's the "old way" of doing things of course.
It fits in to the rest of the "movement" or trend currently happening: Thick (web) clients that do everything and the kitchen sink (including auth. See JWT in arb HTTP headers instead of cookies), SPAs so that there is no server side page rendering (this must all be done in the thick web client you see), document databases instead of SQL so the "frontend" devs don't have to worry about schemas, SPAs so that we break half the bloody internet because we now need to retrofit browser navigation using hashtags, everything has to be an "API" now because we can't convey data using server-rendering, etc.
Honestly, just that navigation thing alone is nuts and I can't believe we ever allowed it to be imposed on us. At this point, I'm afraid to touch those buttons on a new website without first trying them to learn their specific behavior on that site.