Is it because western tradition ignores them? Or because they think it's not philosophy, but mysticism? Or because they are afraid of losing ground to a superior thinking?
Ignorance, prejudice or proselytism? Or something else? Or all of them?
Great question. This will be an incomplete and potentially unsatisfying answer, and I will be interested to see other answers, but here are five answers to start with:
With all that said, I have long thought that anglophone philosophy could benefit from further engagements not only with Chinese philosophy but also with Indian and other traditions. And there are certainly philosophers currently, actively working on establishing those conversations. So perhaps our ignorance will be diminished somewhat!
I think there are several contributing reasons (as someone who has both published and taught both canonical Western philosophy and Chinese philosophy).
The style of classical Chinese texts does not lend themselves to the same sort of classroom experience. It's a pain in the butt having to explain some of the most important passages in Chinese philosophy and it's hard to see how to do so in a way that can enable students who cannot read Chinese and have not studied the tradition to do the same. Conversely, it's not that hard to get someone able to argue with something Plato says. (Modern philosophy is even easier for us to digest in the West).
The primary corpus of analytic philosophy centers on issues that are only tangentially present in Chinese philosophical discourse (unless we mean the part of contemporary Chinese philosophical discourse focused on these analytic questions). Daoism vs. hermits doesn't have much to do with contemporary philosophy of mind. Classical approaches to philosophy of language questions wind up being pretty difficult to make approachable.
Most Western philosophers do not know enough Chinese philosophy to competently teach it and their training has not set them up for that. They would need to learn background concepts not present in the primary texts and teach through those -- but philosophers tend to prefer going straight to the meat of an argument, so they will probably not put the effort into learning this material.
I don't quite agree with ChristopherE's final claim. In fact, causation matters greatly to the following parts of Chinese philosophy: The I Ching is a book entirely about change, The Daoist texts are about whether there is order in the universe and how change happens, the Neoconfucian Zu Xhi in his consideration of 理 (li "order" -- but not 禮 li "ritual") is considering whether there is order and how it works. Now are any of the things they say meaningful as contributions in contemporary discussions of causation? If not, I lack the competency to say where the fault lies.
I think his first assertion is also quite dubious regarding "philosophy." Chinese philosophy only does not qualify if we insist on the historical connection to Greek culture. A properly edited volume of neoconfucianism or Buddhist logic would be sufficiently similar in argumentation and style with medieval texts on logic or religion.
All of that being said, I did upvote his answer because I think it is a moderately good explanation sans those two points.
Chinese philosophy per se might be a bit of a limiter in this question since the question is equally valid applying it to any 'eastern' philosophy, early Indian being another sizeable exclusion.
Am studying Ethics at a Chinese University right now we do have courses in contemporary Chinese as well as western philosophies. My professors on western philosophy are all Chinese and its really amazing to discover how much knowledge they have on western philosophy. One thing that caught my attention is the fact that despite their vast and deep knowledge of western philosophies most of them can not read an English text. During my first visit to the library I realised that they have almost every western philosophy textbook translated into Chinese. Not many Chinese textbooks on Chinese philosophy have been translated into western languages. However I respect the fact that Chinese scholars are currently working hard to overcome this imbalance . With the growing number of Chinese students studying in western universities and western students studying here in China I think this question will soon be irrelevant. So the main reason I think was and is still the language barrier.
Chinese philosophy is poorly understood in the Faculty and this would be both a cause and effect of the lack of study. It is not because it is mysticism because mysticism is philosophy, or can be studied as such. I feel the explanation is partly 'not invented here' syndrome, coupled with the difficulty that if the nondualism that runs through Chinese philosophy is found to be the correct explanation for the world then there will be eggs on many faces in the Academy.
You speculate that it might be 'because they are afraid of losing ground to a superior thinking'. This could be it, but I'm not sure many professional teachers know it well enough to know whether it is superior or not. You also wonder whether it is 'ignorance, prejudice or proselytism? I'd say it is exactly these things.
The failure of scholarship that leads to this situation is a scandal. We have one tradition of philosophy for those who cannot solve philosophical problems and one for those who can, where members of the the former will not study the latter for reasons lost in the mists of time.
It is not just Chinese philosophy that is ignored. It is the entire 'Perennial' philosophy, to which Chinese philosophy makes a significant contribution but which is global and has an even vaster literature. Apparently only people who cannot solve philosophical problems are allowed to teach or be taught in our universities. We praise Wittgenstein for his ignorance and confusion and miss the knowledge and clarity of Lao Tsu. It's a crazy world.
I feel considerable sympathy for students, who may never spot that they have been deprived of any chance of understanding philosophy by censorship and propaganda. It's too big a topic to delve into fully here but your question is a good one and very topical.
Heidegger puts the blame on the loss of the idea of Unity from philosophy that occurred with the Greeks after Socrates. This seems plausible to me. Once we abandon the idea of Unity the best of Chinese philosophy becomes incomprehensible, and history shows that so does philosophy as a whole and the world with it.