It was literally announced to huge fanfare in all of the tech press, and even some of the mainstream press, that Apple was releasing a Journaling app as part of the new iOS. People were going on and on about "wellness" and all the rest of it. It's like complaining that they "silently installed" their timer app on your phone, or their stock market app (which I have never seen anyone use).
It was about as silent as a declaration of intent in front of the world media, months and months before it happened.
I've been using one since about three or four years now with no problems at all - except for one site I was signing up to (I completely forget which) that didn't accept the email. But this was a number of years ago and I have never had a problem since. Also, no one has ever told me they never got my email due to spam filters (as of yet).