Complex sentence: This is most likely because the patrician senators who opposed the law would have been most responsible for enforcing it through bringing prosecutions under it and also by choosing to follow it and thus adopting it into the Roman legal mindset.
Split into simpler sentences: This is most likely because the patrician senators who opposed the law would have enforced it by prosecuting people under it. They also chose to follow it and thus adopted it into the Roman legal mindset.