no idea who you talk to, but the trilogy has sold plenty of copies, enough to make the NYT bestseller list. I doubt that were just D&D players
You are correct. The TSR fiction sold to a lot of people who had never played the game, including a lot of women.
The first couple Ravenloft novels sold well over 150,000 copies in just their first year or so of release, for example, just in print, just in English, and continue to sell in ebook and audiobook to this day. Circa 1990, the average new Dragonlance book would sell at least 125,000 copies in English in its first year or two, the average Realms book at least 100,000 copies. (Those numbers eventually flipped, as the Realms overtook DL.) All the fiction releases had longer "tails" than the game products--they would continue to sell through in the market for months and years, diminishing over time, but still selling okay. Individual books and certain series would sell really well and then continue at that high level for a long time, without trailing off as much as other titles: the original six DL novels, the early Drizzt books, and so on. Many of the books were also translated into several languages.
For the early RL novels and the first Dark Sun quintet, series for which I was series editor, I know they sold many times what the core game products tied to the same setting were selling. The same was true of all the fiction, at least through around 1994. Ben Riggs has released some of the comparison numbers. Those numbers are incomplete, but still a fair metric for the difference in sales between fiction and games at the time.
In all, the fiction was, through the 80s and the first half of the 1990s, a very effective gateway to the TTRPG.