Why so little?

[Maglor]

Interesting question. There are a few reasons, I think, though my knowledge of Tolkien and his motivations is not nearly as thorough as some around here, so you might want to take this with a grain of salt ;-) . Some may be my own conjecture.

My understanding is that Tolkien originally wanted to publish some of the older First Age tales of his legendarium fairly early on, but publishers would have none of it. Instead, he was asked to write a follow-up to The Hobbit and The Lord of the Rings is what came out. And then after seeing its popularity, he set out to comprise a suitable Silmarillion for publication but, sadly, never finished the job.

Tolkien was always a perfectionist, tweaking his "histories", harmonizing the texts to match both each other and his ever-evolving vision (as seen by the multiple editions of The Hobbit and The Lord of the Rings). I think that has to be a contributing factor to why many of his greater tales remained unfinished and unpublished. That, along with the focus of his writings later in life, with essays on his creation taking precedent over the crafting of full-blown narratives.

Was he content with what was ultimately released to the public? I haven't studied Tolkien in-depth, but it wouldn't surprise me if, in a way, he was. His writing carries the air of an authentic history, with allusions to past events and figures that would seem obscure to all but the die-hard reader (Sil, UT, HoME, etc.). He didn't shy away from leaving some aspects of his legandarium shrouded in mystery, the answers of which existed in his mind alone (e.g. Tom Bombadil, the Blue Wizards, etc.).

As much as I would have loved to see some of the epic stories from his posthumous works come to full, rich completion, part of me enjoys that we the readers know them just as the characters in LOTR would have known them: ancient tales whose heroes (and villains) live on in mere story and song, existing as achetypes and legends that aren't (and maybe shouln't) be viewed in present tense. That sense of history is something I think Tolkien both appreciated and strove for in his conception of Middle-Earth.