Is 'Q' required in 'dataToExpQ' of 'template-haskell'?

Hi! Why 'template-haskell.Language.Haskell.TH.Quote.dataToExpQ' does not have a type @Data a => (forall b. Data b => b -> Maybe Exp) -> a -> Exp@ ? The argument of type @a@ does not contain variables (this makes no sense), so 'Q' is not used for generating names.