Different algorithm for the formation of excerpts of the recording, what is the reason?

Question

WordPress

Faced such a problem.
I'm using the better-anchor-links plugin to automatically generate "content" from h2-h6 headings.
It has an option to automatically insert content at the very beginning of the post.
BUT
you can also directly specify the place with a shortcode.
So.
For some reason, when forming excerpts, he / or WordPress itself ignores (cleans up) all shortcodes and after that it works (when forming an excerpt) inserting content at the beginning of the post.
The question itself does not even concern this, or rather not quite this.
When viewing posts from the main page and from any category
on the main page, the shortcode is not cleared or the content is cleared but not added,
but in the heading, the shortcode is cleared and the addition to the beginning of the article and to the passage, respectively, works.
QUESTION
Why does it work differently on the main page and in the headings?