If a thesis is supposed to show the examiner how much you know, then it makes sense to try to show as much as possible.But this is not the point of a thesis. The point of a thesis is to demonstrate competence in your research field.If you're really good, it shouldn't be possible to say everything you know. The way to show your expertise is to select the most relevant and interesting points from your extensive knowledge.You have to leave things out. It's the only way to get the thing done.

See also

How to write a thesis you can defend easily