Remy Sharp digs into the history of the web and describes why the
<p> tag doesn’t need to be closed like this:
<p>Paragraphs don’t need to be closed <p>Pretty weird, huh?
Pre-DOM, pre-browsers, the world's first browser was being written by Sir Tim Berners-Lee. There was no reference implementation and certainly no such thing as a parsing specification. The first browser, the WorldWideWeb.app, parsed HTML character by character applying styles as it went along. As opposed to today's