I agree. One would be ignorant to think that SDC isn't competing with Six Flags for St. Louis area dollars. However, I believe three major problems are preventing SDC from winning that battle.
1) Proximity. It's an obvious one, but Six Flags is simply far more convenient to get to for St. Louis area residents/visitors.
2) SDC is a niche destination. Many people around STL know that SDC is a mix of demonstrations, shops and shows with some rides sprinkled in. While it's right in the wheelhouse of many, I would argue that there are an equal number of folks who have no interest in driving four-plus hours to visit a park that isn't simply full of rides. As much as we love it, it's just not for everyone.
3) Misconception. I can't tell you how many people around STL are baffled when I tell them my wife and I went to Branson and SDC for the weekend. Many have either never been, or have not been for a very long time. They don't realize how much both have to offer for everyone and how vastly different both are now compared to several years ago, much less a couple of decades ago. This is a marketing/advertising issue as far as I'm concerned, but a real world barrier that's keep many from many from even dabbling with the thought of making the trek to SDC once a year, let alone bucking up for season passes.
OK, obviously more people who live in St. Louis are going to go to Six Flags. That's a given. BUT, what about people in Tulsa who don't have much in the way of a major theme park? Are they going to go to KC which is about 4 hours away, or are they going to go to Branson which is about 4 hours away? OKC - I don't know if there's a theme park there or not, but from what I do know, I don't think there's much of one, is there? If not, then same question. Columbia, MO which is about 2 hours from both St. Louis and KC or are they going to spend the extra couple of hours to drive to Branson? You see, it's all about proximity. Yes, some places HAVE a theme park... but others really don't have much of one.
And yes, I COMPLETELY understand where you're coming from with people not knowing about SDC! I work in the tourist industry, and I get people ALLLLLL the time asking me, "what's Silver Dollar City? What is there to do there? Is it just rides for kids?" Seriously. So yes, I get that, and yes, I agree that it's a marketing thing, and SDC SHOULD run ads on KC, STL, Tulsa, OKC, Chicago, Little Rock television stations and other major cities to get the word out more. When I lived in KC, I don't think I EVER saw an SDC ad. So yes, you're right... they should do that. But despite that, there are a lot of people who DO know what SDC is all about, but still choose to buy season passes at a theme park based on price of ticket and what that park has to offer. And for many, SDC doesn't cut it on either of those (especially if you have really young children).