Functional Programming in Java, Second Edition: p. 35 "Refactoring to Narrow the Scope", code

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The following code is given on p.35

        final Function<String, Predicate<String>> startsWithLetter =
                letter -> name -> name.startsWith(letter);

maybe it would be better to use parenthesis to highlight the right-associativity:

        final Function<String, Predicate<String>> startsWithLetter =
                letter -> (name -> name.startsWith(letter));

Underneath the Function is used as follows:

final long countFriendsStartN =
   friends.stream()
      .filter(startsWithLetter.apply("N"))
      .count();

The use if apply() is not highlighted. Evidently this is the apply() of the Function interface and thus a shard of Java clunkiness - it just means “call this function with that argument”.

Why can’t I just write:

final long countFriendsStartN =
   friends.stream()
      .filter(startsWithLetter("N"))
      .count();