Why is Kant so difficult to understand?

Why did you answer me? What makes it almost incomprehensible?

*not

What should be answered? He writes unclearly.

If I may add - there is a new translation of the Critique of Pure Reason, which can be read and understood in any way, by Jeremiah Yuval. At the beginning there is an introduction and a summary of Kant's theory which is like a book in itself (almost 100 pages) and quite clear.
If you want something light (relatively) there is the Open University course book called ”Studies in Kant's Introductions” there the things are written beautifully.

But I would really appreciate a response to the thread starter's question - why are so many masterpieces written in an unclear, cumbersome, and difficult-to-understand manner (I think you also mentioned Popper's book, which is difficult to get through)? Is it just that they just didn't know how to write clearly, or is there something about writing systematically and deeply that comes with such clumsiness?

For some of them, it was an ideology of concealment and directing the text to intellectuals. This is the esoteric concept. Others try to be precise and therefore resort to poor grammar and terminology to escape mistakes and inaccuracies. And some lack writing ability or did not spend enough time on clarity (as Mark Twain wrote, sorry for the length, I didn't have time to shorten it).