I don't particularly follow sales numbers, but my thoughts on things like this are simple: Gamers are not a monolith. What may appeal to some, may not appeal to others.
Not everyone is tripping over themselves to get AC: Valhalla, or Cyberpunk 2077. Publishers can't hold on to games indefinitely, especially as once teams wrap production on one title, they generally shift focus to the next game (unless the game has extra content coming, and even then, it won't need the manpower of the entire team to produce said extra content, so the bulk of the team moves on).
For every person that's not interested in Immortals, there is another that is. For every person interested in Cyberpunk, there is another that isn't. And so on and so forth. The combination of new hardware releasing, and a lot of rather good titles releasing on top of that (the PS5 had a particularly strong launch line up, and the improved performance in many cross gen titles has boosted sales of some older and current titles), has definitely had an effect on some gamers spending. In these instances, the legs of a title are more important than just day or week one sales. No doubt Immortals is going to get a nice price drop in time for the holidays, and it's a fun, family friendly game that will be a good stocking stuffer for parents looking for something for the kids.
I doubt it had the budget or manpower of an Assassin's Creed title, so I'm sure Ubisoft isn't particularly worried. The game is cross gen, so it will probably sell more on current gen software in the end.
And how many people rushing in to shit on the game's title, or how "derivative" it is have actually played it?
Personally, it was a game that wasn't high on my radar, but once I cleared out some of my PS4/PS5 backlog titles, I caved and bought it using some PSN credit I had. It's actually quite an enjoyable game. It most certainly wears its Breath of the Wild inspirations on its sleeves, but it also has its own style and tone that's very different. It's just a really fun game, to be honest. For anyone looking for something light hearted and that doesn't take itself seriously, especially after a very stressful 2020, as well as a series of hugely serious and emotionally taxing titles (ie, The Last of Us, Ghost of Tsushima, and more M-rated fare like AC: Valhalla and Watchdogs: Legion), a game like this is perfect antithesis. Those not wanting to pay full price for it will wait for discounts, but I don't think it's a game that needs to sell 10 million copies to be profitable for Ubisoft, and I don't expect they imagine it would anyway.
But again, not all gamers are a monolith, and just because Cyberpunk is coming out this week doesn't mean every gamer is dropping everything to get it.
If every gamer liked the same games, well, more games would be selling in stupid crazy numbers. There's literally over 200+ million gamers out there, across multiple platforms, and it's clear we aren't all buying the same things, at the same time, or at all. There's definitely overlap from some gamers, but different strokes for different folks and all that.
For me, personally, I passed on AC: Valhalla, but bought Watchdogs: Legion (it was another title I got at discount, along with Immortals, though I have yet to play much Legion). I'm not particularly interested in the Viking setting of Valhalla, and I'm also still playing through Odyssey, so I don't think I'll get Valhalla anytime soon, if ever. I also got Cyberpunk 2077 (also discounted thanks to PSN credit I had just sitting there unused). I had room in my budget for a few extra games after the PS5 launch, and I chose those 3 (Legion, Immortals, Cyberpunk). Other gamers will have a different list of titles to snag leading into the holiday season. So far this year, there have only been a handful of titles I've played full price for, as I've either gotten them on discount, or used up accrued gift card credits for them.
I definitely recommend Immortals if you enjoyed Breath of the Wild, like Greek mythology, or just need something light hearted and silly to play going into the holidays. I know I did, so it's been a nice breath of fresh air (along with Astro's Playroom and Sackboy). I'm genuinely impressed by how much fun I'm having with this game. I think it'll surprise the people that aren't offended that it dared to tread the same ground as Breath of the Wild. 🙄🙄