The answer to this question clearly explains the standard rule that when you have multiple quoted paragraphs, each new paragraph starts with an opening quotation mark, but only the final quoted paragraph has a closing quotation mark at its end.
This Wikipedia article on Quotation Marks agrees:
Quotation marks are used for multiple-paragraph quotations in some cases, especially in narratives. The convention in English is to give opening quotation marks to the first and each subsequent paragraph, using closing quotation marks only for the final paragraph of the quotation [ . . . ]
However, neither explains why this is the standard practice. What good does it do? What is it trying to avoid? What harm would occur if it were ignored and people put both opening and closing quotation marks on each adjacent quoted paragraph?