To play this game I already have a Google account and a Stadia Pro account, and paid $10 for the game. On first launch, you are then required to create a Ubisoft account. Why is this so? This is a horrible user experience. I refunded the game about 3 minutes after purchasing.
Stadia is "just" a platform. The publishers, in this case Ubisoft, are responsable for the game and if they required other account such as you expierenced. In some cases this opens other possibilities like cross-plattform-gaming, cloud save games, etc, pp..
It's the same expierence as you buy games on Steam. 🙂