Is Returnal a system seller? Was Control? I'm not sure that criteria matters, and actually anecdotally (which doesn't count for me) Horizon is absolutely a system seller. Not like a naughty dog game of course, but more than most games.
It's not just a racing game either to
@esmufc07 point. This isn't 50 cars on 30 tracks with nice polish. It's a huge open world with tons of variety in landscape, dynamic weather and seasons, shared open world, and loads of different options for gameplay (racing, open world roaming, challenges, barn finds etc.) and brilliant multiplayer including full game co-op, multiplayer modes (like tag, king of the hill, capture the flag), a battle royale and a huge builder/creator sandbox. There's an incredible amount of content there, as well as incredibly tight and fun racing and/or open world experience depending on what you're looking for.
It's as deserving of GOTY as anything else I agree it's less likely to get the recognition from publications as GOTY itself, but that's just based on arbitrary criteria rather than the quality of the game itself.