You can read whatever you want. No one is forcing you to read "for fun."
It seems you mean this: https://en.wikipedia.org/wiki/Obscurantism#Deliberate_obscurity.
Therefore, I interpret the question as why read a philosopher whose work is generally obfuscating? Granted, when you get into philosophy more and more, there will be an increasingly amount of advanced ideas and concepts. At higher levels of abstraction, from say practicality or applicability, comes tightened diction. Philosophy, just like electrical engineering (EE) or medicine, can get very arcane with new and challenging argot.
Just as an EE professor who made her doctorate in communications EE does not know the specialty of power EE, so it is with philosophy. Professors do not know everything about all of philosophy. One of my philosophy professors did not know much about contemporary ethics. That doesn't mean much: Philosophy is a hugely diverse field. For that reason, I see this question as naive. It is truly a group of small questions, per ________ major works, rooted in ignorance:
Aristotle (Classic Greek)
Why read/study Nicomachean Ethics? Well, right off the bat, it's easy with Squashed Philosophers.
Why read the Critique (of Pure Reason)? Duty-based theory (deontology) is a fundamental building block for contemporary ethics, such as Habermas's discourse ethics (short film). Although, few completely read the elephant. Point: Professors do not assign whole texts as this. Only sections.
Why read the Phenomenology (of Spirit)? He is the "philosopher's philosopher." Gregory B. Sadler has an awesome series: Half Hour Hegel. Furthermore, if you think a certain text is too hard, look for commentary about it. Some books and online resources even have neat in-text annotations.
Why read the Communist Manifesto? His works are also available on Squashed Philosophers. Additionally, a Google search--esp. with "filetype:pdf" "site:edu"--will provide good results.
Why read his "magnum opus, Being and Time (Sein und Zeit)"? (SEP)
If you haven't noticed by now, I didn't actually answer any of the small questions (i.e, why read ________ philosopher). That's your job. You have the tools.