Luther's original intent was not to cause a schism, but over time he and other reformers saw themselves as course correcting. We commonly see the Protestants as being the ones to split away, but they saw the Roman Church as doing so.

Also worth noting: prior to the Reformation, average congregants could not read the Scriptures for themselves and neither did many understand the Mass because the commoner did not know Latin. The reformers were so effective partially through their shrewd use of technology. Luther bypassed the gatekeepers and wrote directly to the common German, in his own tongue, leveraging the printing press in a way no one had done before. Other reformers did the same. In fact, without the Reformation, there would not be mass literacy. Anyone being able to learn to read the Scriptures for himself comes with the risk of various interpretations and divisions. But I would argue for all the complications this has wrought, it was worth it.