The problem with these places is what happens, when you need to hire people to build your company. The tech world is full of impressionistic statements like 'they have a startup scene,' but when you start getting numbers on available talent, you'll see you're putting yourself in a bad position.
To take an example where I have better data, people have commented on the vibrant and growing startup scene in Santiago, Chile. Maybe it is vibrant and growing, but the total number of people professionally employed in software development (devs, testers, manager, product managers, etc.) is only about 2000.
Split that 2000 into 50 different companies (and 50 tech companies would often be held up as proof of viability for the location), eliminate the high percentage with the wrong skill set for your company, and how likely is it, really, that you could build an engineering team of 20 and sustain that in the face of attrition over time?
St. Louis isn't going to have more than a few thousand of the same sort of people. Most of them are also not products of local universities with strong engineering programs relevant to most of the kinds of software behind most tech startups these days. The supply therefore is not growing at a steady rate or being replenished.
75 startups in one location? What happens, when the half that make it past the founder stage need to hire 3-4 people? Not only are there only a few available devs of any skill level available for each, but they all have dozens of options on the same block.
For startups, a higher percentage of engineers in an area employed by companies of 50-people or less actually makes hiring harder. In such a situation, they all have options of more or less equal value, and you have little to distinguish yourself from the others. The fact that SV has Google, Yahoo, Mcsft, etc. alongside a ton of mid-sized and smaller companies makes it easier.
If you've ever tried to recruit for a startup, think about how often you bring up ownership, autonomy, "startup culture," etc. as selling points? How well does that work in an environment, when nearly everyone already has that where they are?
This is just a quick set of reflections, but the overall point I hope is made. The truth is that staffing your startup is one of the most brutal forms of competition your business will experience. You're one of many, many players competing for an extremely scarce resource that very few founders even know how to identify, qualify, or retain, once they've got them.
If you ever plan on building your company beyond a small team of friends and local referrals, you should be doing everything you can to stack the deck in your favor. The Bering Sea may be an expensive and crowded area for gold prospecting, but you're still more likely to find gold there than in Lake Michigan.