Yes but those trailers aren't made then targeted at the marvel studios subreddit. They're made for mass market appeal. A direct only showing Joker and a couple new modes isn't going to sell fighters passes because most people watching already have it were as a shorter trailer aimed at people who either haven't bought the game yet or aren't as into Smash as we are would make more sense for something like this.
And a Direct showing Joker (and possibly another fighter) will make a net profit off of production costs from people who chose to buy those Fighters/the whole pass. There is no reason for them to break this trend of how they've handled basically every Smash reveal. You are way overthinking it.