Why do the pupils of EFL feel difficult to learn English?

Like any foreigh language - it's a new turf, so there are challenges and new ideas

Because they don't work hard enough!

English is one of the easiest languages. Since it is an international language, efl students feel over whelmed while learning it. The efl teachers should first work to remove the anxiety.

may be becouse every thing in the biginng is difficult , may be becouse of thier culture

It is primarily because any non-native speaker of English process language/information in their native language. They tend to literally translate the sentence in its structure and grammar into English while English has its own set of rules. 

This can be overcome by a lot of exposure to English through environment and audio/visual medium. 

I thinks that it's difference from one student to another.