The game had to start dying down at some point. It just doesn't fit in with Ubisoft's business model of yearly sequels. I'm surprised Siege lasted this long to be honest. Expect the content to be reduced in frequency as the game steadily reaches it's end point. We already kind of see that already with no new maps and recycled weapons. Also, not too long ago they were talking about preparing for the future of Siege when there would be less seasons in a year so there's that.
That isn't really what is happening. I understand that it may appear as if the game is winding down, but that is pretty far from the case.
We are actually in the process of growing the team. We have a few people, Xavier and Alex among them, that have been working on Rainbow Six Siege for almost a decade. They no longer feel as if their direct involvement is necessary for the game to continue to grow, and are going to step away from it to let new people take the lead.
The people stepping up have been a part of the Rainbow Six Siege team for a while now, and have an exciting vision for where to take the game. Leroy mentioned briefly that he wants to focus on creating features and content that impact all players, and that is the direction we are headed.