I think it's a combination of OW still being not as widely known and played as e.g. Civ6 or HK and it's depth, balance and good AI. I have now more than 100h OW played...and I'm still feeling like a beginner. It is much harder to post about sucessful strategies or just give helpful tips, if you still get hammered by the AI or subtle mechanics surprise you every couple of turns. The good balance and the interwoven mechanics add to this, as it is much easier to point out how to min-max something which already feels broken like e.g. maximing the rewards for plundering in Civ6 by doing this while running the corresponding policy card compared to discussing whether and if when and how to lay waste to the battlefield in OW.