Featuring your IPs on a direct competitor's platform isn't perceived as being good for your brand. If you're going to dabble in putting your exclusives elsewhere, starting with the PC makes a lot more sense. It's not a direct competitor. Most Xbox gamers are potential Playstation owners. Not necessarily the case with PC.You reframed the question. Why not release HZD 3.5 years later on Xbox? How is this obvious? Microsoft develop Minecraft on PS4. Sony, until recently, didn't put big hitters on PC either. Now they do, why not Xbox too?
An All or Nothing approach doesn't make sense. Why do they have to release it on Xbox? Nobody expects the same for Microsoft, either. You can make your case that they should also consider releasing on Xbox. But an all or nothing approach doesn't really make sense when there's plenty of well supported reasons why Sony is comfortable on occasion putting their games on PC. Especially a tech showcase like this one.