The most surprising thing is that the textbooks haven't been updated. When I was a psych prof this was a commonplace among all my colleagues and even students. It's even common to use this "experiment" as a case study in class to discuss problematic experimental design.

I'm not sure why textbooks haven't been updated, but I doubt the hypotheses mentioned in the article (ignorance, that the authors believe the study, and pressure to keep textbooks short).