I have a custom theme with just a name in its style.css. I've activated it in admin which shows it just fine.

In the index.php just <?php wp_head(); ?> and it doesn't output the line that is supposed to include my main stylesheet style.css:

<link rel='stylesheet' id='my-theme'  href='~/wp-content/themes/my-theme/style.css' type='text/css' media='all' />

It prints out all the other stuff but that line! What would make it not print out my default stylesheet inclusion line?