Well, it IS a Tale as Old as Time......
Sure the game was popular in the late 80s/early 90s, for the gamers. The "world" hardly noticed.
Late 90s was a wasteland, but, eh, we had the rules so, game on
2000s it explodes again, everyone loves the game again. Even the novels take off like rockets. Borders has HUGE cardboard castle displays. Comic/game stores are EVERYWHERE..even the Malls(remember Malls?) Soon enough even "non fans" know about the game too.
2010 things slow down again...4E is not all that great. Comic/game stores close by the hundreds. Book stores like Borders are gone. Novels slow down to a trickle. Everyone knows about "that D&D game" it seems....
2020 5E has brought the game back, though all the stores are gone...we have online.
And..well today