Here's why:
* Gerunds are verbal nouns: They act like nouns but have the characteristics of verbs, like taking objects.
* Indirect objects receive the direct object: They tell *to whom* or *for whom* the action of the verb is done.
Example: "He gave her the book." (Her is the indirect object; she is the recipient of the book).
Since gerunds are nouns, they cannot receive something. They can be the direct object of the verb, the subject of the verb, or the object of a preposition.
Example: "He enjoys reading." (Reading is the gerund, the direct object of "enjoys").
Instead of using a gerund as an indirect object, you might use a prepositional phrase:
* Incorrect: "He gave *reading* the book."
* Correct: "He gave the book *to reading*." (This is grammatically correct but awkward. It's better to rephrase the sentence.)
* Better: "He enjoyed reading the book."