And Chinese is not very phonetic, which means that often you just completely forget how to write a character, if there is no obvious semantic clue in the radical, and no helpful phonetic component somewhere in the character.
Top 2 Because the language doesn't have the common sense to use an alphabet
The English is so easy because of the skills needed to master the writing system are 26 letters and they are written from left to right ,horizontally, across the page, with spaces to indicate word boundaries.
In comparison, Chinese has nothing that corresponds to an alphabet, though there are recurring components that make up the characters.
It can be said that the components of Chinese characters are arrayed in two dimensions, rather than in the neat one-dimensional rows of alphabetic writing.
Top 3 Because even looking up a word in the dictionary is complicated
One of the most unreasonably difficult things about learning Chinese is that merely learning how to look up a word in the dictionary is about the equivalent of an entire semester of secretarial school
Chinese must also be one of the most dictionary-intensive languages on earth for there are various dictionaries.
Top 4 Because there's classical Chinese (wenyanwen)
Classical Chinese really consists of several centuries of esoteric anecdotes and in-jokes written in a kind of terse, miserly code for dissemination among a small, elite group of intellectually-inbred bookworms who already knew the whole literature backwards and forwards.
Top 5 Because there are too many romanization methods and they all suck