People aren’t farming out their dissertations to other grad students (usually). Yeah, once a person is a PI, their grad students do most of the actual writing, but anything written in their dissertation or as a grad student or post-doc is almost certainly all them, especially if they are the first author.
And even once they are a PI or even a department chair or university president, anything they write where they are listed as the first author is 100% their responsibility.
Your post just reads like you don’t really understand how academia works.