为什么<img src>用php编写依赖于用html编写的img src？

When I take out the HTML code below the <?php ?> the webpage does not load anymore. Why is there a dependency on that code below? I am sorry for the specificity of this question, but it is really frustrating me and I cannot seem to independently find an answer.

<?php

    /*Write a function to return an HTML <img /> tag. The function should accept a
    mandatory argument of the image URL and optional arguments for alt text,
    height , and width 
    */
    function html_img ($img_url = "\"https://img.purch.com/h/1400/aHR0cDovL3d3dy5saXZlc2NpZW5jZS5jb20vaW1hZ2VzL2kvMDAwLzA5OS8zMjkvb3JpZ2luYWwvY2hpbXBzLWVhdC1tb25rZXktYnJhaW5zLTAx\"", $alt_text = "\"ronald\"", $height = 400, $width = 1200){


$the_format = "<img src=" . $img_url . "alt=" . $alt_text . " height" . $height . " width=" . $width;

return $the_format;

    }

print html_img();

?>


<!--When the code below is removed, the image is not displayed.-->

<!-- <img src="https://img.purch.com/h/1400/aHR0cDovL3d3dy5saXZlc2NpZW5jZS5jb20vaW1hZ2VzL2kvMDAwLzA5OS8zMjkvb3JpZ2luYWwvY2hpbXBzLWVhdC1tb25rZXktYnJhaW5zLTAx" -->

The image tag in $the_format is unclosed, so it is probably appearing in the markup (view the page source) but it will not be rendered in HTML without the closing > or />