It also requires:
1) having friends who are interested.
2) Reading and math.
3) Willing to be creative and imaginative.
That makes it unattractive to the average person.
These and the same reasons that science has never been popular. Most people don't want any entertainment that requires thinking. Heck most don't even like to get out and play sports, or do easy physical exercise like walking. People are lazing.
Here's another thing that I think has cropped up in the last few years: SCHEDULING. Among gamers, it's incredibly hard to get everyone to have the same amount of time off every week/two weeks for several consecutive hours. Of the non-college attending adults I know, they can only manage one game a month.
Even without attempting a frequent game, getting the guys together once every few months is tough. We all have jobs, most of us have kids, someone is always moving or on a business trip, whatever.
Much easier when we were all in high school or college, or on summer break!
Turn that part around by saying WOW is ridiculously convenient... You can play whenever you damn well feel like (except for patch/maintenance days), and you literally don't have to get out of bed to play. The only scheduling you have to do is for raids and arena (and even those you can PUG as long as you're tolerant of some degree of fail...).
I never had a general problem with scheduling just the occasional 3 or 4 times a year can't come. Well except while I was in the military but we had ways to get around that. But I am an old fart who got a lot of problems by turning my entire family into RPG player.