ZOS just chose not to include the Falmer ruins.



As for developer comments, I can find two.

Way back in 2013, they said: https://www.elderscrollsonline.com/en-us/news/post/375

Q: I'm a mer at heart, and my favorite race of Elves is the Falmer (Snow Elves). I was intrigued by their appearance in TES V: Dawnguard and would like to know: will we learn anything more about their race, history, or culture in ESO? – By Sean Ferrel-Wyman

A: In the Second Era, the Snow Elves are a near-forgotten legend, and the fact that they’ve degenerated underground into the feral Falmer of Skyrim is a deep secret. But secrets can be discovered, and the Falmer may make a future appearance in ESO.


There's been nothing more on the Falmer in game, though of course we haven't had any further Skyrim expansions.


In 2015, an in-character interview as Lady Laurent comments on them here: https://www.elderscrollsonline.com/en-us/news/post/25431

“To the illustrious Lady Laurent of Daggerfall, from a fellow seeker of lost treasures and forgotten lore,

I trust this letter finds you well, though there's no telling, given that couriers in Covenant lands seem to have a terrible habit of forgetting to deliver their messages.

In either case; I am writing to you to inquire if, in your rather extensive travels, you have come across any mention of the ancient Falmer, or Snow Elves, of Skyrim. As any student of ancient history, or any self-respecting Nord could tell you, the Snow Elves were here long before our ancestors ever made the journey from Atmora of old. Having seen the majestic ruins and arcane remnants of the proud Ayleid peoples scattered across Tamriel, one would assume that their Northern cousins in Skyrim would have been similarly advanced, in both culture and spell-craft. As a mage and scholar of Skyrim, I have been scouring tomes and personal accounts for any clue as to what became of the Falmer, and if any ruins or artifacts of their people remain. The potential breakthroughs in spell-craft alone are astounding! (Never mind the wealth and fame due to any who might uncover the secrets of the forgotten Snow Elves). If you have any leads that might aid in my search, please, send word immediately! (Though again, I strongly recommend against using any of the local messenger services.)

I'll be sure to credit you in my next book, should my search come to fruition,

Respectfully, and expectantly,

Asgautr Grey-Wind, Mage of Winterhold"

Lady Clarisse Laurent says, “Physical remains of the long-lost Snow Elves are indeed few and far between—mute testament to how thoroughly the race, and all it created, was eradicated by your ancestors, Mage of Winterhold. At least we Breton nobles had the decency to allow our Direnni oppressors to withdraw to their little island in the Iliac. But you're quite right, any genuine discovery of Falmeri relics or ruins could make a scholar's career. On my visit to the Wrothgarian Mountains I intend to be alert for any evidence our new allies the Orcs may have of former Snow Elf sites, but frankly I am not optimistic."


Obviously, that "I am not optimistic" was borne out with Orsinium's release, as there were no Falmer included.