I disagree.

Some people purposely avoid trailers because they spoil the plot, but go on the subbreddits perhaps to hear news or check on the state of the game.

That why the spoiler tag exists. Just because a game releases a gameplay or a trailer pre release, doesn't mean it's "fair game". That point is extremely flawed simply because not everyone watches trailers.

Even games like RDR2 have been out for a couple years and people still use the spoiler tag or avoid spoiling altogether.

Your point of it being "fair game" because of gameplay trailers is a weak one. Only the truly dedicated would watch them. An even larger amount probably joined in the hype a few months before release and joined the subbreddit to follow the game.

Reddit has a spoiler tag for a reason. A person dying is a pretty big spoiler, and honestly it took away from my experience because someone on reddit couldn't press 2 buttons to mark spoiler.