To clarify, the British complaint about the streaming market is almost guaranteed to be the cause of this, but nothing in that article claims exclusive streaming rights. Ubisoft will be guaranteed a right to stream the games (on seemingly any platform but maybe mobile), but the language used any time the article quotes the blog post seems to imply that they'll still be able to also offer them themselves or license them elsewhere. Their point of emphasis is that it prevents Microsoft from exclusivity of streaming rights, not that Microsoft still doesn't have them or can't also license them to others. (It also mentions Microsoft abiding by other existing rights deals).