While everyone is piling on with the untested hypotheses, here's mine:
The madlibs form is just too wordy. Whereas the username/password field pair is not only less wordy, it's an idiom: I've seen those fields, in that arrangement and that order, thousands of times over the last decade. I barely even have to read the captions at all.
Not that this hypothesis, or any of the others, matters. The point of this article isn't to design a better form. It's to show us how to design a better form.
The madlibs form is just too wordy. Whereas the username/password field pair is not only less wordy, it's an idiom: I've seen those fields, in that arrangement and that order, thousands of times over the last decade. I barely even have to read the captions at all.
Not that this hypothesis, or any of the others, matters. The point of this article isn't to design a better form. It's to show us how to design a better form.