Why is the Twitter code being rewritten in the html news add form?

Question

Twitter

When editing a news item, the Twitter code inserted into the html

<blockquote class="twitter-tweet" data-lang="ru">
  <p lang="en" dir="ltr">
     .<a href="https://twitter.com/DeclanMcKenna?ref_src=twsrc%5Etfw">@DeclanMcKenna</a> played one of the shows of the year at <a href="https://twitter.com/KOKOLondon?ref_src=twsrc%5Etfw">@KOKOLondon</a> on Friday! <br>
 <br>
     See full pics by <a href="https://twitter.com/cfaruolo?ref_src=twsrc%5Etfw">@cfaruolo</a> here - <a href="https://t.co/nRbj83rIM8">https://t.co/nRbj83rIM8</a> <a href="https://t.co/msMrKGCdUI">pic.twitter.com/msMrKGCdUI</a>
  </p>
   — EatYourOwnEars (@EatYourOwnEars) <a href="https://twitter.com/EatYourOwnEars/status/927506954733412352?ref_src=twsrc%5Etfw">6 ноября 2017 г.</a>
</blockquote>
<script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>

Rewritten to this:

<twitterwidget class="twitter-tweet twitter-tweet-rendered" id="twitter-widget-0" style="position: static; visibility: visible; display: block; transform: rotate(0deg); max-width: 100%; width: 500px; min-width: 220px; margin-top: 10px; margin-bottom: 10px;" data-tweet-id="927506954733412352"></twitterwidget>

Why?
There is one Twitter widget on the main site. Does it give that effect? Or how?