im not sure what ur getting at exactly, but...i think ur meaning to say that more game players know about oblivion than landfall.
This is correct. More people know about Oblivion than landfall. More people played the game than read the book, and very few people have read the loveletter compared to those who've played Oblivion.
in that case, ur making the book and the loveletter (/and some other obscure lore tidbits) non-cannon.
Incorrect. I'm saying that the reason why they didn't mention the novels in the teaser trailer is because the novels themselves are
A) less well known.
B. incomplete.