I think I have a clue in my own case.
Before role play gaming I came out of wargaming. Going back to when I was seven or eight years old, sometimes playing and sometimes observing war-game recreations of famous historical battles and campaigns while under the tutelage of my uncles and great uncle.
So my experience may be "older" (in that respect) than many of you, and different from many of you. I was aware of store-bought modules (for D&D), and sometimes used them in a form that was adapted to my setting and campaigns.
But from the very beginning I started out playing D&D with the assumption that I was creating my own world and that my world was to be used to host coherent, large-scale campaigns of interconnected scope and interest.
Most of my buddies played this way too, designing their own worlds and matching campaigns within those worlds. The worlds and the campaigns that took place in them were sort of inseparable. Though one buddy used Greyhawk, he created his own campaigns in that setting. Everyone else made up their own worlds and campaigns.
I've never really thought about it in this context before but I suspect I (and we) did it that way because of our familiarity with war-games, and the associated extended and complex campaign ideal. (We often even played Risk this way, creating campaign types and we would have all day and all night Risk games with shark-steaks and fish fries and bottle-rocket fights and night-time ambushes of each other to conclude the games. (There was no LARPing back then but we would camp out and then break into teams with wooden weapons right before sun-up and then attack each other with ambush assaults and guerilla operations. Those were great times to be a kid because you could do all kinds of things that nowadays, unfortunately, kids can't do because everyone is so geared up by terrorism. Not that I'm not in favor of maintaining good security against terrorism. I am. It's just that nowadays kids can't be as relaxed about what they do because of somebody sees them running around the woods in camo attacking each other somebody will call the cops. But I grew up in a running fight in the country and we all loved it. A certain kind of innocence and fun has been lost and to me camp-outs, fights in the woods, D&D, Risk, wargaming, going fishing, tracking animals, frostbite and exposure, waking up being attacked by wild pigs, it all bled together. They weren't separate things, they were all part of the "campaign" of being a kid and enjoying yourself and exploring things. It's a shame some of that has been lost. But I digress.)
To me to be playing, wargaming or role play gaming, meant to be "on campaign," which meant involved in a large-scale, complex operation of battles (or adventures in RPGs) which were components of a larger war (or campaign in D&D terms).
Also the idea of campaigning to me always presumed an objective or set of objectives. You didn't just campaign to go a'Viking. You campaigned with an objective you intended to achieve.
To me wargames were strategic (it was all about the group objective - the army or military group objective) and the RPG was all about tactics (that is about the small party or individual objective) but both were ultimately about the objective and the strategy (the overall goal).
Occasionally we'd game just for the hell of it, or for comic relief, but in the main, we gamed to a purpose. To reach some goal or get killed trying to. Figuratively speaking.
Edit: Come to think of it I've often wondered if people who had prior, or simultaneous experience with wargames and role play game might not have different experiences with either or both than those with just experience in role play gaming.
I've also often wondered if people who grew up in the country and people who grew up in the city might not have totally different role play gaming experiences due to their differences in environment (it seems a logical conclusion anyway.)
I sat in on one game in college, run by a kid who had grown up in Atlanta.
Part of the adventure was wilderness and his descriptions of how things operated in the woods was laughable to say the least, though I don't think anybody pointed out his errors. You could tell the closest the guy had ever come to the real wilderness was traveling the back roads on the way to Disney World. I didn't dislike the guy at all, he just had no idea of what survival or the wild was like in any respect.