I've seen this mentioned a couple times. As I understand it, this is from some interview or online video, right?
If it's not in the books, you can't expect people to know this. I certainly didn't, and hadn't heard of it for the vast majority of the time 5e is out. "We told you in a video on youtube" is a terrible way to disseminate rules for a game that is played (at least by many) with actual physical books. If that video isn't directly linked to by the online rules, it's a terrible way to disseminate the rules for player who use the electronic tools, too.