I think the main reason given is if you think something needs a br tag, the content before and after should probably be in p tags or something else. That's at least what my 2am brain remembers reading somewhere some years ago.
<p> tags are for paragraphs. If you’re trying to break in the middle of a paragraph or sentence, they’re the wrong tool to use. Also, they’re not flexible across breakpoints like <br> tags are.
