For example, natively getting a list of children is `el.children` but natively getting the parent is `el.parentNode`, not `el.parent`. Meanwhile, natively getting a list of classes is `el.classList`, but when I'm getting children I also get a list, so why not `el.childList` instead of `el.children`? Natively cloning a node is `el.cloneNode(true)`, so now I have to remember what `true` is for and whether I want it or not (surprise: the default changed between JS versions, so the "optional" argument must always be included for compatibility!). Probably the most commonly used line in web JS in jQuery is the terse `$('selector')` but natively is the mouthful of `document.querySelectorAll('selector')`.
So while jQuery isn't strictly necessary, it's certainly a nice syntactic sugar, and IMHO a more sane and consistently-designed API than native. It's a great choice for developers who want avoid big frameworks like Vue and get as close to plain HTML/JS as possible, but still want a pleasant JS development experience.