Mathematical notation can be spoken out loud. Hence, you can include it in a sentence without breaking the flow of that sentence. For the more complicated equa

Mathematical notation can be spoken out loud. Hence, you can include it in a sentence without breaking the flow of that sentence. For the more complicated equations, it becomes harder to unambiguously pronounce them, and the ideas are more separate anyway. Hence we need to break them out. Moreover, I disagree that mathematical notation is a rigorous grammar. Notation is used to be consise, to represent ideas so we can work on them. Precision is only added to resolve ambiguities that are hard to resolve based on the surrounding text. One can make notation fully unambiguous, but that often comes at the cost of consiseness, and thus clarity.