The stereotype that most hardcore gamers are either loners or below the age of 21 isn't a stereotype. It's just the way things are.
As one gets older and life responsibilities begin to pile up, your time for gaming has to dwindle; it's just a matter of simple math, as there are only so many hours in the day. Provided you don't let the hobby consume your life (which usually doesn't happen to most normal people), most 35-year-olds don't have the time required to be a "hardcore gamer."
And that's true even if you don't go by time as a definition for "hardcore," and I don't. I believe anyone is hardcore if their primary hobby is gaming, but can one even say that when their time is so limited? Can you even have a primary hobby given all the demands you face on a daily basis? This seems like a relatively boring subject until you start to see how this impacts the industry. Even the older gamers, the "hardcore," those who grew up with a certain "old-fashioned" form of interactive entertainment, have less time to play and therefore, they buy less. Hence, a lesser demand for forms of gaming that are dying out.
It's just a natural progression. So for those of you who are around my age going, "hey, there are lots of us who still love side-scrolling action and pure adventure games and turn-based RPGs," I have only one thing to say: No, there aren't. There are lots of us who have fond memories of those game styles and wouldn't mind seeing new products with those old-school mechanics. But we have to admit we might not even be able to play it if it did arrive. We can't compete with the kid in college who has absolutely nothing to do (you'll learn you had nothing to do in college when you get older, kiddies), heading to every midnight launch.
And because gaming is big business, the publishers just don't care about the dedicated who only used to be dedicated and would like to be dedicated again but haven't the time or money to manage it. Sad but true.