The All-Star break is a convenient line of demarcation in the baseball season. It gives us the familiar first-half/second-half designations, even though the halves aren’t split exactly down the middle. And, of course, it provides the basis for the familiar “tale of two seasons” trope. Where would we be without that story structure?
There isn’t a similar dividing line within each half of the season. There’s no such thing as a first half of the first half, at least not in the way we talk about these things, or, say, a website like Baseball-Reference tracks them. There are no stories about a tale of two halves within one half of the season.