It would be simple to point out that English is a very hard language to learn. Complex tenses, cases, irregular verbs, a huge vocabulary, spelling that truly is just random at times and obtuse at others, plus pronunciations that just don’t fit the Chinese tongue. English is a difficult language.
However, China is awash with English teachers. It is a compulsory subject in school from primary school through to the end of university and even included in many post-graduate professional examinations. There are resources online, on the TV, and in every bookstore in the country. Also finding an English school or teacher, even a native teacher, is a simple task in most Chinese cities.
Thus English isn’t that difficult for Chinese people. Rather it is one of the easiest to learn because all the things one might need in order to study are available.