[Grammar] What are the differences between these two sentences?

[羡鱼-Xianyu]

orignal sentence: If the scientists hadn't been so careful, they might never have discovered a cure for the disease.
changed sentence: A cure to the disease might never have been discovered had not the scientists so careful.

Question: Why should the preposition 'for' in the orignal sentence be 'to', when it was changed to the second sentence? Thanks a lot, in advance.:?:

 

[Tdol]

I would use 'for' in both sentences.