There's more than one value of obvious involved; people get different answers. Some of the popular ones are that this is Aule and Yavanna, or unspecified Maiar, or, well, there are theories.

My favourite is to recognize that there was a point in time where Tolkien wrote "all I have to do is get them to Rivendell" and for that scope of Hobbit-sequel, the visit with Tom and Goldberry and the Barrow-downs would be a different structural part of the book, and certainly a reminder of the great age of the landscape the hobbits are moving over.