Not all airports have JetA, because not all airports can even support jets/turboprops (by and large the biggest consumers of JetA).
If there were some aircraft that could only run on 94UL, then airports would have more of an incentive to carry two kinds of avgas. But with that not being the case, it’s a bit of a chicken-and-egg game. Why would an airport make the investment into 94UL tankage (as an example) when there wouldn’t even be a guarantee that they’ll sell enough to make the investment worth it in the long run? Especially when we have cases like Burke and others that are under threat of closure because of the perception that they don’t bring in enough income.
But rather than having a hypothetical discussion about this, why don’t you just go to your local airport manager and make the case that they should sell a second avgas. If it’s such a slame-dunk case, it should be easy to convince them to do so. And if you’re successful at that, it can be used as a template for others to do the same.