Why the text fields are not getting disabled="disabled" in colorbox popup?

Why the text fields are not getting disabled="disabled" in colorbox popup?

I'm using PHP, Smarty , jQuery, Colorbox - a jQuery lightbox plugin, etc.
for my website. Now I'm displaying some output in a popup which is
generated by using " Colorbox - a jQuery lightbox plugin". Now I want to
disable all the text fields present in this popup when the form loads but
if I go to the HTML source of page the disabled="disabled" attribute from
the <input> tag gets removed and the text boxes are not getting disabled.
Can you tell me why this is happening? For your reference I'm putting
below the code which will display the data in a Colorbox pop up.
{if $subject_topic_questions}
{foreach from=$subject_topic_questions item=subject_topic_data}
<div class="hidden">
<div id="topics_{$subject_topic_data.subject_id}"
class="c-popup">
<h2 class="c-popup-header">Select Topics</h2>
<div class="c-content">
<input type="hidden"
name="subject_names[{$subject_topic_data.subject_id}]"
id="subject_names"
value="{$subject_topic_data.subject_name}">
<h2 class=""> {$subject_topic_data.subject_name}</h2>
<div class="c-tbl-wrap">
<table width="100%" cellspacing="0"
cellpadding="0" border="0" class="c-tbl">
<tbody>
<tr>
<td>
<p class="custom-form">
<input class="custom-check"
type="checkbox" name="" id="">
<label class="blue">Select All</label>
</p>
</td>
{foreach from=$difficulty_levels item=diff_levels
key=dkey}
<input type="hidden"
name="diff_levels[{$dkey}]"
value="{$diff_levels}">
<td width="22%"
align="center"><strong>{$diff_levels}</strong></td>
{/foreach}
</tr>
{foreach from=$subject_topic_data.topics
item=topic_diff_level_data}
<input type="hidden"
name="subject_{$subject_topic_data.subject_id}_topics[]"
value="{$topic_diff_level_data.topic_id}">
<tr>
<td valign="middle">
<p class="custom-form">
<input type="checkbox"
class="custom-check"
name="{$sheet_type}_topics_{$subject_topic_data.subject_id}[]"
id="{$sheet_type}_{$subject_topic_data.subject_id}_{$topic_diff_level_data.topic_id}"
value="{$topic_diff_level_data.topic_id}"
onChange="enable_topic_ques('{$sheet_type}',
'{$subject_topic_data.subject_id}',
'{$topic_diff_level_data.topic_id}');
return false;">
<label>{$topic_diff_level_data.topic_name}</label>
<!-- <input type="hidden"
name="topic_names[{$topic_diff_level_data.topic_id}]"
value="{$topic_diff_level_data.topic_name}">
-->
</p>
</td>
{foreach
from=$topic_diff_level_data.difficulty_level
item=diff_level key=key_diff_lvl}
<td valign="middle">
{if $site_id=='ENTPRM'}<em>Total
{$diff_level.question_count}</em>{/if}
<input type="text"
name="{$sheet_type}_{$subject_topic_data.subject_id}_{$topic_diff_level_data.topic_id}_{$key_diff_lvl}"
id="{$sheet_type}_{$subject_topic_data.subject_id}_{$topic_diff_level_data.topic_id}_{$key_diff_lvl}"
maxlength="3" class="mini"
value="{$diff_level.added_no_questions}"
disabled="disabled">
<input type="hidden"
name="{$sheet_type}_available_questions_{$subject_topic_data.subject_id}_{$topic_diff_level_data.topic_id}_{$key_diff_lvl}"
value="{$diff_level.question_count}">
</td>
{/foreach}
</tr>
{/foreach}
</tbody>
</table>
</div>
<p class="center"><a href="#" class="c-btn
fnClosePopup">Done</a> <a href="#"class="c-btn
c-gray-btn fnClosePopup">Cancel</a></p>
</div>
</div>
</div>
{/foreach}
{/if}
The main code you need to consider is as below from the above code:
<input type="text"
name="{$sheet_type}_{$subject_topic_data.subject_id}_{$topic_diff_level_data.topic_id}_{$key_diff_lvl}"
id="{$sheet_type}_{$subject_topic_data.subject_id}_{$topic_diff_level_data.topic_id}_{$key_diff_lvl}"
maxlength="3" class="mini" value="{$diff_level.added_no_questions}"
disabled="disabled">
Can you tell me how the disabled="disabled" attribute gets vanishes after
page load and if there is any way to apply to it, please tell me. Thanks
in advance.