Answer 1

Because it cannot contain anything in it, see, the elements with ending tags can contain something in between, but <progress> doesn't.

<p>A paragraph</p>
<a href="...">Hyperlink</a>
<span>Some text</span>
<button>Caption</button>

All the above can contain something in between opening and ending tags, but <progress> wasn't meant for that. It instead shows a progression graphically.

It is not about inline or block element, <span> for example, is an inline element, but it allows content in between the opening and ending tags : )

Answer 2

Godsmercy because progress tags are inline tags.
Just simple
Don't be create confusion of yourself
😊

Answer 3

Godsmercy because some tags in HTML are inline tags like <img>,<br> etc so they dont require closing tag.
While block level elements like <form>,<table>,<div> needs closing tags