Because they learn to read sentences from the beginning-that is, to break sentences.
Moreover, ancient Chinese pays great attention to phonology, and punctuation is well-founded.
Punctuation marks were introduced from the west in modern times.
Generally speaking, writing brush strokes is not allowed, but since the Republic of China, some literati and calligraphers have used it when writing brush strokes, so some people use it now, which is also a form.