Why didn't Tolkien do more with the Stone-Giants?

Question

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?

Answer 1

I think the main factor is that stone giants don't fit into Tolkien's Middle-Earth legendarium very well. All other beings have an explained origin, including the Ents, but stone giants just seem like a generic fairytale construct.

Answer 2

Not necessarily a bigger role, but giants appear in at least one writing of Tolkien's from c.1967.

Tolkien was putting together a guide to translators of The Lord of the Rings, and he was explaining the origin of many of the place names to help guide whether they should be translated or left as is.

For Tarlang’s Neck (a pass in the white mountains that Aragorn and the Grey Company travel through), Tolkien had drafted out a legend involving a giant named Tarlang.

... Tarlang in local legend was the name of a giant of ‘long ago’ of one of the giants who in ‘ancient days’ had built the White Mountains as a wall to keep Men out of their land by the Sea. But Tarlang, while carrying a load of rock on his head, tripped and fell, and the other giants used him to finish the wall at that point, leaving his neck lying southward, while his head and the load made up the Sjouthern] mts of the ridge, [?called] Tarlangs, that separate the plain of Erech from [?Lamedon],
_{The Lord of the Rings: A Reader's Companion - Book V, Chapter 2}

He then rewrote this note to be more descriptive:

... But owing to the facts that lang ‘neck’, though frequently used geographically, was also applied to the neck of men and animals, while Tarlang was a not uncommon man’s name*, there grew up a local legend to explain the name. It was said that when ‘in ancient days’ some giants were building the White Mountains as a wall to keep Men out of their land by the Sea, one of them called Tarlang tripped and fell on his face and as he was carrying a heavy load of rocks on his head he broke his neck and was killed. The other giants used his body to complete the wall at that point, but left his neck lying southward, leading to the three mountains of the spur: Dol Tarlang ‘Tarlang’s Head’, Cûl Veleg ‘Bigload’ and Cûl Bin ‘Little Load’. The break in his neck was shown by a depression in the ridge, near the junction with Tarlang’s Head, over which the road went.
_{The Lord of the Rings: A Reader's Companion - Book V, Chapter 2}

Of course this is just a "legend", but giants being part of the mountains does seem to fit with the giants we meet in The Hobbit, and I think this is the only time Tolkien returned to this concept.