JSON Feed: RSS, but JSON

JSON Feed is a feed format like RSS and Atom, written in JSON instead of XML. I stumbled upon it while playing with a project that required converting RSS to JSON.

{
  "version": "https://jsonfeed.org/version/1.1",
  "title": "My Example Feed",
  "home_page_url": "https://example.org/",
  "feed_url": "https://example.org/feed.json",
  "items": [
    {
      "id": "2",
      "content_text": "This is a second item.",
      "url": "https://example.org/second-item"
    }
  ]
}

Why are we still using XML for feeds when JSON seems to be a more direct, streamlined option?