Back in the days when WordPerfect was (arguably) the world's leading word processor, it did not do master documents very well either. Although (arguably) it did it better than Word has ever done. The problem I think lies inherent in the concept of multiple files and the I\O involved. I\O has been, and remains, the leading cause of corruption.

IMO Word itself is robust enough to handle most situations that one can think of that in theory master documents are supposed to handle.