It could be argued that the total number of 'real' labels in the data is indeed large (e.g., because every verb exhibits its own syntactic patterns) and that a small number of labels is just an arbitrary decision of the corpus annotators.
most linguistic theories agree that there is a prototypical level of generalization that uses concepts such as Noun Phrase and Verb Phrase, a level which consists of at most dozens of labels and is strongly manifested by real language data.