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.