Nested paragraph selector - why doesn't it work?

Question

css

There is this HTML code:

<p>Text 1</p>
<p>
  <p>Text 1</p>
</p>
<div>
  <p>Text 3</p>
</div>
<b>Text 4</b>
<b>
  <b>Text 5</b>
</b>

and CSS:

p {color: red;}
p p {color: green;}
div p {color: blue;}
b {color: grey;}
b b {color: blue;}

As a result, we have on the page:

You can see an example here: https://jsfiddle.net/12mb0014/
It turns out that the nested selector: does not work, although the nested selector: works. Why?
p p {color: green;}
b b {color: blue;}

Answer 1

and you look through the inspector, as a result, the browser renders your layout. A paragraph cannot be nested within a paragraph.

Answer 2

paragraph cannot be placed within a paragraph)

Answer 3

I wonder what forced such nonsense to write