No one is going to open a restaurant where the target market is “people who don’t go to restaurants”.

???

When you open a restaurant, the only target market is people who don't go to your restaurant. Looking into how to expand your business to people who don't already go to restaurants is absolutely a valid line of inquiry that companies persue all the time. Maybe the reason they don't eat out because it's too expensive, and you can appeal to them with lower prices. Maybe the reason they don't eat out is because they don't know how good your food is, and you can address that with free samples. Maybe they have dietary restrictions and you can appeal to them by adding vegan or gluten free options. Restaurants, like any business, are constantly looking for ways to break into new sections of the market. So your analogy falls completely flat.

Look at, for example, Little Caesars which at least back when I was in school had cheap ass $5 pizzas, they tasted like shit but they were $5 so being a broke ass college student I ate there all the time when I might otherwise have not eaten out at all. And that's why they focused on keeping the price low instead of making it actually good. Because at $5, even groceries wouldn't be much cheaper.

Likewise, if a political party is uninterested in appealing to people who don't already vote for them, it must mean that they're satisfied with their current level of support. Which, considering the Dems lost the last election, doesn't exactly seem to be working. And what, do you think you'll have better luck trying, again, to appeal to "moderate" Republicans? Let me know how that goes, lol.