Because the people that care about design don't really care about the App Store (they care about products instead), and the people that run the App Store don't really have an incentive to try and make dramatic changes in something that, from their perspective, is wildly successful. Change might break things, especially when operating on the scale that Apple is (just think of what the load must be on the App Store).
That's true. And if you care about this issue, you could try appealing to Apple executive leadership (emailing tim cook, or running a PR campaign designed to get Apple executive leadership to see your arguments).
