I suspect some botched market research or misguided agenda towards xbox. If the goal was primarily to make the most money it would have made more sense to prioritize PC where all the players will be.
Nobody is buying a new Xbox to play PSO2. The handful of people that would feel compelled to get in early on Xbox would go get a second hand one.
Xbox has been known for not getting many Japan games on the Xbox One until very recently. Getting PSO2 which is a popular game to the West was their way of showing their Xbxo gamers they are going in the right direction investing more into getting popular Japanese games over to the West. If they had the game 1st on PC then it doesn't give the console owners that satisfaction they are still the top priority.
As to why people feel neglected it's more than likely because of NDA or simply SOJ telling them when they can talk. Look at game leaks that happen. The game is pretty much already ready but the company never talked about it because it wasn't the time they wanted to.