It is logical for laying out text because if a text is larger than what fits on a screen, you want lines to be no wider than the viewport width and instead have

It is logical for laying out text because if a text is larger than what fits on a screen, you want lines to be no wider than the viewport width and instead have the text expand vertically. So width is constrained by what is available but height determined by what is necesary for the content. The CSS flow layout is designed to make text content readable by default on a variety on device dimensions.