Can someone write a doctoral thesis without reading any other doctoral thesis in the same field?

As far as I know, I did.

I did original work for which there was little in the literature and so I built a methodological platform from scratch. While I went through a lot of documents, I don’t recall any of them being a thesis or dissertation.

Generally, if a thesis or dissertation is high enough quality, it will be memorialized in the form of a journal article, book chapter or book. And those are the types of things I looked for.