Present perfect and present perfect continuous in negative sentences

[JaneGothic]

English Grammar in Use says:

"We say 'I haven't done something since/for ...' (present perfect simple)
I haven't seen Tom since Monday. ( Monday was the last time I saw him)
Sarah hasn't phoned for ages. (=the last time she phoned was ages ago)"

An exercise in English Grammar in Use Supplementary Exercises contains this sentence:

"I'm not surprised that he has failed the exam. ______ (he/not/work) hard recently"

In the keys the answer is he hasn't been working. Why present perfect continuous? Not present perfect simple?

 

[Tarheel]

I would say:

I'm not surprised that he failed the exam. He didn't study.

Or something like that.

 

[emsr2d2]

"English Grammar in Use" says:

"We say 'I haven't done something since/for ...' (present perfect simple)
I haven't seen Tom since Monday. (Monday was the last time I saw him.)
Sarah hasn't phoned for ages. (The last time she phoned was ages ago.)"

Remember to put book titles in quotation marks or in italics.
Note my other corrections above. I don't know if the errors appeared in the book or if you just didn't copy them exactly as written.

An exercise in "English Grammar in Use Supplementary Exercises" contains this sentence exercise:

"I'm not surprised that he has failed the exam. ______ (he/not/work) hard recently."

In the keys key, the answer is "He hasn't been working". Why should the present perfect continuous be used no question mark here Not rather than the present perfect simple?

It's not a great exercise. "Recently" can be used with both the present perfect simple and the present perfect continuous. It depends on whether the action is completed (and was completed not long ago) or if the "recently" also includes the present moment.
I'd have chosen the answer in the key but "He hasn't worked very hard recently" would also be correct.