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Looking back on it, what got me initially hooked on any game I played when I was younger was a nice-looking ad I had encountered on some unrelated website. It led me to investigate it, read about it and then join it if it seemed nice. When I joined said game, free or subscribtion-based, it usually had a decent population of other people who had encountered it in such a way as well.
Thing is, ever since I downloaded adblock on firefox (you know, to remove those youtube video ads like everyone else)...well I obviously haven't seen any more ads. That got me thinking, how can any game be successful when they are limited in their advertising? These days advertising only goes as far as some youtube video, and once that video loses its front page it cuts off the population that didn't see it. Considering the amount of people who use firefox these days, and people who have downloaded adblock to get rid of the youtube annoyance, advertising is pretty much invisible for any new person that uses the ff browser. Even if they create some facebook page they can't expect people to find said page unless they hear about it from someone else.
You could say "if it was popular or good enough people would spread it", but I think we all know gamers aren't very social people.
I am sure everyone knows what I am talking about when I say that new games these days just don't garner any new players. Once you get the starting batch from youtube/mmorpg sites and those leave, it pretty much goes downhill. I am not saying it is the major reason for lower population of MMO players, but wouldn't you agree that it has contributed to the decay?