3.76 pronouns as objects

It is normal to use this prepositional structure when the direct object is a pronoun such as 'it' or 'them'.

This is because pronouns usually refer to things that have already been mentioned, that is to information that is known to your hearer or reader. In English, new information usually comes at the end of the clause. So, when the indirect object is new information and the direct object is not, the indirect object is put at the end of the clause.

Note that in informal spoken English, some people put the indirect object in front of the direct object when both objects are pronouns. For example, some people say 'He gave me it' rather than 'He gave it to me'. Both pronouns are unstressed and both refer to information that is already known, and so it does not matter what order they come in.