Yeah because most people do not find chess, go or backgammon particularly fun. Sorry to burst your bubble if you thought they were somehow perfect games.
BGG rankings tend to be pretty good. I find they rate co-op games, sequels, kickstarted games and very heavy games a bit too highly. But apart from that they're good.
I don't know why you would expect Backgammon in particular to be highly ranked. It's got more strategy than most highly random games (e.g. cribbage) but it's not fun, at least not compared to the many many better board games that exist now.
As I mentioned in another comment, I expect most of these classic games would do even worse if they were released today. Struggling to find an audience, ranking down in the lower reaches on BGG. The communities around them and their cultural heritage are what they’re really about, and I doubt that you could bootstrap them back up to their current prominence if they showed up out of nowhere today, based solely on the strength of the games per se. Though, to be fair, the majority of top-100 BGG games will be all but forgotten in 100 years, too.
All the more reason Crokinole—a far less well-known classic game than backgammon or chess or go—ranking so highly is remarkable.