Synopsis is a pure persuasion game. Your job with a synopsis is to persuade a reader to invest their attention towards your writing.
It consists of three things; credibility, if I trust the writer that he'll not butcher at least the beginning of the story, how it reads, if it has that "I know what I'm doing" vibes. If it doesn't show the mask of the implied author properly, readers will feel that the story they're about to read is cringe, and scroll off. Incompetent and those who used too much ButlerGPT die off there.
Emotional appeal, as in if the story shows, not tells that it has feelings, be it tragedy, call to adventure, or whatever those smut writers are cooking with appendages. There's certain feel to each story, it must not be too emotional (or else it will drown the credibility) or too mechanical (credibility will tank), so it's a tightrope, on which you infer the ideal reader you think of, and write for him.
And the last is logical. How the tropes are used, if they're cliche, how they're deformed to make an interesting start, how it is delivered. It follows the Gricean maxims; quality of information (each sentence must precise of the story), quantity of information (each information must be not too long or too short, enough to know), relation of the information (go off topic, and you've lost a reader), and manner of information (how it's delivered, see the credibility). It is where everyone suffers, because the audience you're writing to is too random. You need to find the ideal reader of your story to make it informative enough, for them to says "huh, interesting", and click "read".
Synopsis is communication. If you can't communicate ideas, you'll never have a reader. Know yourself and know your reader, and you'll persuade them to read every time.
