See, there have been a lot of posts like this in the thread, and they can read a little silly. People had lives back then. They did not think of life as slow paced. (And people have always imagined an earlier, simpler time, its a cliche). Even in the realm of geeky-hobbiess, there where other RPGs and hobby games and other geeky things you could do. (Join the Society for Creative Anachronism, own 50 different avalon hill wargames, watch Star Wars at a theater still showing it 5 years after it came out). But again, we know people are buying and playing D&D. And again, in another thread here some of them are playing it a lot.
Gamers have magnitudes greater opportunities for their roleplaying fix today than they did 30, 40 years ago. When I was in high school I had a group of friends who played Everquest. I saw them as potential D&D players. I involved several of them into the game, and while some of them were decent enough roleplayers, I doubt they have touched a d20 since. What they were looking for in my D&D game, they could find in their Everquest game. And they could find it on demand, in their underwear, at 2 in the morning. I would imagine all of them have continued to play games with roleplaying elements continually since then.
Had this been in 1980 instead of 2000, they would have had very limited means to scratch their RPG itch. D&D was it, until Wizardy and Ultima came along. They could certainly relive their interest in medieval life through the SCA or ren faire, or indulge in their wargaming impulses through an Avalon Hill title. But until RPG's started to cross pollinate and influence other mediums, they couldn't wield a vorpal sword or cast fireball. Much of the success that early D&D had, if not all of it, was due to it being a fad, and it being a near monopoly in terms of reach.