The truth is that, Facebook suppresses YT videos posted on that platform. Facebook wants you to post videos natively on Facebook. If you post a link to a YT video, Facebook's algorithm will shadowban it so that it is not shown to people, while letting you still see it so you do not know that it is shadowbanned. There are ways around this, but Fb generally does everything they can to keep people from seeing YT links. A YT link takes people off of the FB platform, and FB does not want this because they make money from showing ads. Facebook has their own advertising platform and are not part of Google ads.
Facebook is a Pay to Play platform. If you want to promote something on Facebook, they want you to pay for advertising. Facebook wants you to give them your content so they can make money from it by posting ads on it, and then they also want you to pay for them to promote your content, so they can make more money off of it.