Sentence Correction

Hello,

This is taken from MGMAT SC Guide (5th edition), page 61.

We need to correct the parallelism error:

The students did poorly on the test more because they had not studied than the material was difficult.


Answer:
The students did poorly on the test more BECAUSE they had not studied than BECAUSE the material was difficult.

I was wondering why the following is not correct:

The students did poorly on the test more BECAUSE they had not studied and less BECAUSE the material was difficult.


I was wondering if you can please assist? Thanks a lot.

Best Regards,
Sri

Well the meaning of both the sentences are not the same.

The first and correct sentence actually negates the material aspect and puts all the blame on lack of preparation of the students.

Your sentence says that the material was also a cause but to a lesser degree than the lack of preparation.

I hope you understand the difference in meaning of the two sentences.

There is a change of meaning..

Its an Idiom question...More because of X than because of Y.