Didn’t exextly understand, but elementor save the post html in the content without the css just in case you want to remove the plugin in the future.
Let me explain by example:
I start with a blank page, edit this page in Elementor and add a section with three cols and each col get an Image Box. After saving the page and going back to the WordPress editor I will see this code in text mode
<figure><img src="http://wp452/wp-content/plugins/elementor/assets/images/placeholder.png" alt="Sample Image" /></figure>
<h3>This is the heading</h3>
Click edit button to change this text. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.
<figure><img src="http://wp452/wp-content/plugins/elementor/assets/images/placeholder.png" alt="Sample Image" /></figure>
<h3>This is the heading</h3>
Click edit button to change this text. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.
<figure><img src="http://wp452/wp-content/plugins/elementor/assets/images/placeholder.png" alt="Sample Image" /></figure>
<h3>This is the heading</h3>
Click edit button to change this text. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.
If I save this page within the WP editor I not getting the the columns and all the other Elementor formatting.
Hope with this example you know my problem. Thanks
In WP editor we stored just the content without any extra CSS classes and something else. If you want to get the columns and all other Elementor formatting, you need to use with Elementor in frontend also.