A dissertation is a long formal document which you write if you want to get the Doctor of Philosophy degree. This work os required for this degree.
You need to research do a lot to write such type of work.
Actually, sometimes teachers ask services to help with writing. I work at HandMadeWritings and we have a lot of orders from educators. Custom writing services
like handmadewritings.com provide quite good custom writing services for lecturers and professors so sometimes they decide not to do a research by themselves but order it.
So be careful:) Maybe your PHD got his degree not in a fair way