Here it's typical that a thesis will be printed as a book, and it's that book that will be evaluated. For PhDs, there's a doctoral defence in front of a committee, peers and other interested parties and they're all given the book.
Usually the process for ordering books is that you send them a PDF with embedded fonts inside it, and it's made at the university's printing house. They will handle distribution etc. So you really, really want it to look right at the first go.
There's been some progress the past few years now where you get to preview the book somewhat, but one surefire way to get it right is to use something like LaTeX. It used to be one of few WYSIWYG solutions out there. And it used to be really hard to do certain required things in e.g. Word. For instance skipping some page numbering and doing others in roman numerals etc.
This answer makes sense to me, because it is rooted in a functional need - the need to have a printing house consume the results successfully.
Some other comments are oriented around aesthetics ("taste") or the state of other tools (Word, etc.) which I understand but those issues are more personal.
WYSIWYG means what you're editing looks like the end result; LaTex and Typst are at the opposite end of the scale, being languages that compile into layout. No, a preview window does not count as WYSIWYG.