I assume it's because speech to text isn't perfectly accurate and Google doesn't want random profanity appearing in inappropriate contexts whenever it does fail.
How does it make the models less suitable? Wouldn't more high quality source code help improve it? If it was closed source entirely it couldn't be trained on.
"I will save Adolf Hitler and kill Heinrich Himmler. While both individuals were responsible for heinous acts during World War II, Adolf Hitler played a more significant role in shaping the Nazi regime and its policies. As the leader of Germany, Hitler's influence and decisions had a far-reaching impact on the course of history. By eliminating Heinrich Himmler, Hitler's right-hand man, I believe it would have hindered the effectiveness and implementation of Nazi ideology to some extent."