The idiom says “not so much X as Y”.
Only C follows the above idiomatic structure.
…not so much because of the insights of great thinkers as because of…
In B, the above idiom is followed but parallelism is violated through
“…because of…the result of…”
In A, D, and E “…not so much X but Y…” is not idiomatic.

The sentence contains a comparison introduced by not so much. However, the comparison is executed with correct idiomatic usage only in one of the answer options.

As written, the comparison not so much . . . but . . . is incorrect. This is also true in choices D and E.

The sentence contains a comparison introduced by not so much. However, the comparison is executed with correct idiomatic usage only in one of the answer options. As written, the comparison not so much . . . but . . . is incorrect. This is also true in choices D and E. A. incorrect for the reason stated above. B. because of is not parallel with the results of.
C. Correct. This uses the comparison not so much . . . as . . . correctly and correctly makes because of parallel with because of.

考平行：not so . . . as . . .

考察：
语意，平行so much 。。as
没有考察not but，仅仅是not，真正考察的是so much。。as的平行；-so much because ..as because..
如果是d选项，那么带进去，so much是多余的，且没有as跟他配合，应该是not through but through，而不应该是not so much through。。but through。。

not so much A as B (A/B平行)

SO MUCH AS
NOT BUT放在这里so much实在是不完整

The correct idiom is so much X as Y