A concrete example then. Commonly want to prevent form submission default behaviour.

Vanilla

  <script>
    const form = document.getElementById("form");
    form.addEventListener("submit", event => event.preventDefault())
  </script>
  <form id="form">...</form>

React

  <form onSubmit={event => event.preventDefault()}>...</form>

Vue

  <form @submit.prevent="onSubmit">...</form>

React's API has guided the developer to learn about events. If they move outside the React ecosystem they have transferable knowledge. As someone unfamiliar with React, but used to the DOM you're surely comfortable here. Yes, the syntax isn't identical to how you might use this in vanilla JS, but it's clearly the same concept. It's just been made a little nicer to use - the sugar.

Vue's API has reinvented the wheel. There's one place this syntax is useful and one place alone - Vue itself. It hasn't used my existing knowledge, or pushed me to become more familiar with the platform upon which I'm building. That's not sugar, that's a new language.

I've probably got the vanilla example wrong - when you don't do it frequently it's not the most ergonomic thing in the world. React takes that API, doesn't deviate far from it, and makes it easier to use. Sugar.