Among some people, there seems to be a burning need to explain D&D's continued success in some way, any way that doesn't involve it being successful because lots of people like it and enjoy playing it. The attempts to evade the most obvious reason why something is successful get surreal at times. For a while, there was an almost superstitious belief in the power of advertising.
Of course lots of people like it and enjoy playing it.
The question that is posed is why there seem to be virtually no other rpg that is just as known and as much played, despite the obvious existence of a lot of other rpgs that people
also like and enjoy playing, and that is where those arguments come in.
I agree that ads is not the sole reason though:
Even if someone say they don't know of any tabletop-rpgs, there is still a possibility that they have heard of Dungeouns & Dragons.
And a lot that play rpgs knows
only of D&D, and still a bunch of rpg-players that knows of other rpgs still only play D&D, from force of habit, it is the only game the group will play, they think the others are dull (with or without actually having tried them), and/or they actually prefer the rules, the setting, the whole package.
Some might want to try other rpgs, be it Vampire, Cyberpunk, CoC or Champions, but find no one nearby to play anything else than D&D, because of the above reasons.
I guess there are equivalents of gaming groups that just play WoD or Shadowrun, but those are rare, compared to the D&D groups.
And among the groups that play several, D&D is often one of them.