Upvote:7
It basically comes down to tradition.
There are three major divisions of the Decalogue, in order of date. To compare these divisions, see Wikipedia. The dates are from this article.
The Philonic division is used by most Orthodox and Protestant churches, except for Lutherans. It's the earliest recorded division, and very similar to the Talmudic division. The Talmudic division is the one adopted by Jews, and is probably based on earlier rabbinic tradition.
The Augustinian division came centuries later. It was chosen as the official Catholic division by the Council of Trent in the 16th century, and also by Luther at about the same time.
It's probable that the Early Church used the Philonic or a similar division of the Ten Commandments. That's probably also why most Protestants choose to follow it.