Because the Bible was written by dozens of men (if I say “authors”, I’ll get a “you’re wrong” answer) across dozens (??) of generations.
That, in addition to the Bible only recently being translated directly from the Aramaic and Greek texts directly into English or other common languages, as opposed to only from Greek to Latin… adds to some confusion, along with different sects of Christianity.
Different persons have different understandings based on a “sound bite” that appealed to them. For example, I like dropping the “Woe to you, scholars of law… for you have hidden the keys…” bit, due to the nature of my tangling with “the law”. I also have a few other favorites that explain how Christ was far different from what most people likely imagine Him to have been like. “Do not think that I have come to abolish the law, but to fulfill it.” Very good stuff when talking about Constitutional Rights that our society has forgotten.
Also, I can attribute the lack of understanding, considering the abundance of modern translations from original texts, to people who just don’t care, or are confused because the Christians of Old will not adapt to new “technologies” and “discoveries” in understanding discrepancies in translations. The “full of grace” bit is somewhat of an example. Catholics require this to be in the Bible, because of tradition, even tho it was never in Scripture. Some folks just don’t want the Truth.
If we really wanted to understand scripture, then we would. But most are too busy dealing with the troubles of modern day life to deal with “obsolete” knowledge. What would the point in that be? If only the CC promoted the translation that people are “most” likely to understand. One does exist.