Most people are not deep thinkers, and if you're trying to get something complex or subtle across then a message that another deep thinker might have no problem with might simply be too much for most people, whether due to lack of natural ability, lack of skills, or lack of a willingness to try to understand, interest or open-mindedness.
I wonder what you're trying to communicate, and to whom. Many people tell me that I communicate very well (usually when we're communicating through writing/typing etc.) but many people say that they don't understand me, too.
I have often observed groups of people, many of whom have difficulty understanding me when I try to talk of something complex or subtle, who seem to have no problem communicating with each other in spite of them contradicting themselves and using trite popular phrases nearly devoid of meaning.
Whereas most people seem to ask little of their ability to communicate factual information (as opposed to social or emotional information) it seems that many on this site ask a great deal of their ability to do this. Even if we are much better at this than most people, it stands to reason that we might still encounter more difficulties than most people.
People with 4x4s of unusual ability will tend to get stuck more often than someone who drives a low-performance sedan to the store and back and asks no more of it than that.
Keep in mind also that communication is a two-way street, a cooperative venture. They are also failing to communicate with you. It is likely that you are putting in an effort to bridge the gap, whereas they may not even be aware of the gap and are putting in no effort at all. They are used to communicating with their own kind, you are having to communicate, and learn to communicate, with them.
Maybe you're truly bad at communication, I don't know the details. But there are plenty of reasons for communication to fail other than your lack of ability. When communication fails it can be very difficult to know why for sure, sometimes both parties are unaware that they've even misunderstood each other. At least you're not there.