Advisor says I shouldn't expect to finish thesis soon, but won't offer specific feedback on what is missing; how to react? I have a rough draft of my PhD dissertation, on which I was working on and off for about a year, but mostly I was doing other coursework. I have about 90 pages so far.

My dissertation advisor tells me that what I should do is pretty much make sure it is well-written and apply the theory to a few examples. By my estimates, if I go berserk on this, I can finish all that in under one month.

However, the dissertation advisor says that usually, it takes about 3 years to complete a dissertation in my department, and I should not expect to complete it soon. Also, he says that the level of my draft was intermediate (some time ago) and not yet advanced (but he hasn't reviewed the current one yet).

When I ask or suggest about expanding the scope of the dissertation / adding additional chapters, the dissertation advisor says he does not think it is necessary.

So, it appears that the dissertation is almost complete, but I should not expect to complete it soon. How should I interpret this apparent contradiction?
My PhD advisor once told me that one aspect he considers when rating a thesis is how much the candidate did try to go beyond the initial idea or goal. If they are like "I solved the initial problem, here's the thesis, I just want to finish a fast as possible" then they will earn an intermediate grade at the end. Only if they try to go beyond the initial problem, try to at least estimate the further implications or steps or apply the outcome of the initial problem to further problems, they really can earn a top grade.

To my experience, to successfully finish a physics PhD within roughly a year, you have to have had really great luck to find something really excitingly new that provided a huge progress to your specific field. In most cases after one year you can't even tell for sure what the final focus of the thesis will be. Those applications of the theory to some example cases can easily take up more time than the whole development of the theory as there might come up issues and flaws that you were not expecting. Also their importance is not necessarily reflected in the number of pages they make up in the final thesis.

Therefore it seems to me, that you are somewhat belonging to the first type of people mentioned above who are just heading to leave before really having understood the implications of what they were working on.