You're almost assuming that the derivation of western legal traditions in large part from Roman law was a conscious choice or decision over other alternate systems that were less "developed".

It's basically tautological, but the reason for the Latinisms in modern western legal language is simply that they were derived in part from Roman law. Legal traditions and systems generally don't emerge overnight or immediately, and even important watersheds like the Juris Civilis or the Code Napoleon are built on existing legal traditions.

This isn't because other legal systems or traditions were 'inferior' or 'less developed'. Modern Western legal systems might be said to be a mix of Germanic and Roman systems more than anything else.

There is also a problem with the idea of 'Roman legal system' - which one do you mean? Roman law was not some monolithic unchanging system that existed for a thousand years, and itself developed and changed over time. The image of Roman law given through say the Juris Civilis isn't necessarily reflective of Roman law or legal practice throughout Roman history, but a deliberately crafted rationalisation of Roman law created in the 6th century.