Comparison view is about reviewing the changes to this one file.
The repository definitely has many more revisions as evidenced by the fact that when I go to Source Control > History, I see many commits.
Yes, but the majority of those are not commits involving a change in the state of this file, so you are not seeing them in this part of the interface. And rightly so; that would be pointless. You are being shown here everything there is to show, i.e. the log for this file. Every version of this file in this branch contained in the repository is shown in this interface.
Now, having said all that, part of the problem is that this really is not a great interface. It's cute, and it's nice as far as it goes, but if you are trying to review and understand your project's history as a whole, it isn't all that helpful. Personally I almost never use it. Try Atlassian's SourceTree; it's free and fantastic. And ultimately, of course, there is no substitute for the command line.