[TheFuzzball]

It could also be that there is a dirth of high quality CSS training data in comparison to JavaScript et al.

I wouldn't be surprised if the negative developer sentiment toward CSS is reflected in training datasets.

[ileonichwiesz]

My guess is it’s because CSS is so dependent on context. Especially layout styles only make sense for a specific structure of HTML elements, which might be stored in an entirely different file and directory.