At How do comments work? it says:
When should comments be deleted?
Comments are temporary "Post-It" notes left on a question or answer.
You should not expect them to be around forever. Once a
clarification has been made, an edit added to the post to include new
information, or the issue in the comment is otherwise resolved, it can
be deleted. Additionally, any comment that violates the comment
guidelines listed above or the Code of Conduct is subject to deletion.
In reality, on most sites, many since-obsolete or guideline-violating
comments don't end up being deleted due to the high volume of comments
posted, but this does not mean that they can't or shouldn't be deleted
in the future.
The comments deleted from the question you asked about were:
When I reviewed those comments, the question and the answer, I came to a conclusion that the asker was satisfied that their question had been (self-)answered, and so I deleted all comments on it then, rather than relying on the comments being deleted at another time in the future.
The aim for all Q&As on Stack Exchange sites is that their "wiki-fication" will lead to only a clear question and its clear answer(s) remaining in the permanent record.
If you ever see a comment deleted that you want to use to improve an existing Q&A, or to start a new Q&A, just flag it for a moderator to undelete it temporarily, so that you can copy its content before it is again deleted.