Responses to your query will vary by discipline. In the arts and humanities, for example, it is much more common to publish your thesis as a book/monograph. This would be an important expectation on a CV. However, in the sciences, for example, it would be unusual to publish a thesis as a book. More typical would be to publish from a thesis, sometimes while you are writing it, in high quality international peer reviewed journals. Personally, given my discipline (accounting and law) I was able to publish aspects of my doctoral dissertation as I went, and then publish an updated version as a book.
A thesis or a dissertation are books! There is no need for duplicating the same work unless the new book goes far beyond the university publications. Good publishers will not agree to publish a book without a great scrutiny.
These days thesis are being uploaded on the university site. So, no need to duplicate it in the form of book as rightly pointed at by Dr Amir. Publisher are also available in the market which will be interested to publish your in the form of a book.
I think the publication of the research work proves that is a serious and right work. On the other hand, the publication of the thesis allows us to present our first research work among our colleagues and it may be the first step to start collaborations in the scientific field with them.
My University publishes the goods thesis in the Institutional repository of the University.