I don't know of systematic research on this but it's consistent with what I've seen in the fields I've worked in (linguistics, psychology, geochemistry). The AlphaGo paper was special because it's a super-hot high-profile topic and the journals don't want to get scooped (remember Nature is in competition with Science, PNAS, etc. for eyeballs). However exciting a conclusion may be for psycholinguistics, it won't get fast-tracked in the same way.

another comment provided a good explanation (see below), now it remains to check the editor

"Conflict of Interest Disclosures: Dr. van Dam received a research grant from the Nestec Company. No potential conflicts of interest relevant to this article were reported." Guys, Nestec own the world's biggest coffee machine company, Nespresso.