Does not only has to be followed by "but also" always ?

I have seen in many standard newspapers such as NY times, wall street in whihc it is not used the way we learn for GMAT .

David Cameron is trying to prove Lear wrong. He wants to demonstrate to the British electorate and the wider world that a smaller, less expensive state could not only be a better and more efficient state. It would also create more room for personal freedom and individual initiative .

Could any exeprt explain whether in GMAT, we should consider options not following not only .. but also in the intended way.

Thanks.