Maybe it doesn't make sense to have duplicated services for the city. I grew up in Tucson. There's a zoo, but it wouldn't really make sense to have 2 zoos. Likewise with the Sonoran Desert Museum. There are also unique locations to visit. There's 1 Titan Missile Museum. There's 1 Old Tucson Studios. There's 1 Biosphere 2. They are spread out on opposite ends of the city. There are a bunch of hiking spots that are all different, and people don't want to go to the same one over and over.

Then you have things like the air force base or the university. They're important for the economy so you may work at or near them, but for the most part you don't really want to live directly adjacent to them. Fighter jets are very, very loud all day long (my mom lived where you could see the runway right behind her house when I was a teenager), and the military is known to dump very nasty chemicals for their training exercises. University students throw parties, and there's more crime in the area. For a few years, I lived a little over 2 miles from the university, and I had my bike stolen out of my backyard. In the further out part of town where I grew up, that was completely unheard of. Some of the downtown parks are mostly full of homeless adults. The parks where I grew up were mostly full of kids/teenagers.

So there's reasons why you might want to live within a ~30 minute drive of a denser area with services or work, but without having to actually live near a dense area. And your day-to-day services are already spread across most of the city, so you don't need to travel for those. I get the impression that many cities have a similar dynamic.