Let’s note a couple of things.
1. Each card stands alone
You don’t need to connect them together. They work together, but they don’t require holding each one in your head in order to make sense of them all as a whole.
2. Each phrase is very short
No more than 3 words per “card”. The professionals know that if the graphic has even a few more words then they’ll start running into problems. The more words there are, the longer you have to leave the card on screen. This can easily wreck the rhythm of your trailer.
But more importantly, if there are too many words on any given graphic, the audience simply won’t read them. They’ve been trained by years of tv commercials and movie promos that the text is only going to be on screen for a very short amount of time.
As a result, if they see a card that has more than 5 words, they won’t even attempt to decipher it. And even if they do try, it’s often going to be to the detriment of the next thing they see or hear during the trailer. They’ll still be thinking about that long list of text they were just shown.
This can create a domino effect that leads to confusion as they miss important story beats that contextualize other parts of the narrative later on. Remember, we need to be cautious about giving the audience too much information, thus overstimulating them to the point that they tune out.
Their main function isn’t even always the message they contain. They’re often more important as a tool to break up the story and allow easy transition to different parts of the movie quickly.