Why YouTube quality options look the way they do
Above 720p, YouTube stops shipping a single combined file. Video and audio are stored as separate adaptive streams, which is what lets the player switch resolution mid-playback without reloading. A downloader therefore has a choice: hand you a progressive file that tops out at 720p, or hand you the separate high-resolution tracks.
Grabnode lists what YouTube actually exposes for the specific video, in plain language, so you can see at a glance whether a 1080p option exists for that upload rather than being promised a resolution the source never had. Older uploads frequently max out at 480p or 720p simply because that is what was uploaded years ago.