In The Hobbit, the heroes shelter from a storm in the mountains and see a group of stone-giants throwing boulders at each other.
The Stone-giants were out, and were hurling rocks at one another for a game, and catching them, and tossing them down into the darkness where they smashed among the trees far below, or splintered into little bits with a bang.
-The Hobbit, Chapter 4: "Over Hill and Under Hill"
Later, Gandalf considers asking a stone-giant to block up the entrance to the Goblin Town (which suggests that at least some stone-giants are relatively nice guys).
"I must see if I can't find a more or less decent giant to block it up again," said Gandalf, "or soon there will be no getting over the mountain at all."
-The Hobbit, Chapter 6: "Out of the Frying-Pan into the Fire"
But as far as I know, stone-giants don't appear in Tolkien's writing after this. They would certainly be as interesting as the Ents, or at least nearly as interesting, so I am wondering why he didn't do more with them.
Did Tolkien ever discuss why stone-giants don't play a bigger role in his stories?