Hollow Knight = An indie game from three developers from Australia that nobody knew before Hollow Knight, was made by crowdfunding and become popular only because of the world of mouth
Metroid = The 8th instalment of an IP from one of the worlds biggest game publishers that probably got more marketing and advertising on its first weak than Hollow Knight on its lifetime
I strongly advice you to review your assertions because those games weren't even remotely in the same ground when it comes to sales potential when they were released. Hollow Knight is already among the best selling indie games of all time, Metroid Dread is likely to miss the top 20 best selling Switch games
You strongly advise me to review my assertions? What is this, some drama show like Dr. Phil? Lol chill, it's my opinion.
Metroid Dread is the first game in a long time because the previous games didn't sell well compared to other series(if they did, they would have made more 2d Metroid games despite whatever technological barrier they referenced as being the problem). Metroid 1 sold the best, at 2.73 mil. The rest of them sold 1 mil or more less, with multiple not even topping 1 million according to the database.
It's a LOT riskier for Nintendo to greenlight a full HD 2.5d game made by a much larger team on a niche series than it was for a tiny team to make an artful, less graphically intense Hollow Knight. I absolutely love Hollow Knight's art style, by the way, as I own the game, but it wasn't nearly as expensive to make as something like Dread, so the risk taken here is more impressive for Nintendo.
The price is also a big thing. If Nintendo sells just 1 million Dread copies at $60 each, that's $60 million in revenue. Hollow Knight's full price was/is $15 from what I've researched (further reflecting how cheap to make it was). If it sells 3 million copies that's $45 million in revenue, which is less than Dread will make selling a lot less copies. Plus, Hollow goes on sale a lot more than Dread will (being a first party Nintendo game) so the difference is probably even greater there. Again, Dread impresses me more here.
You are right on marketing, at least for now. Nintendo has talked and advertised Dread a lot, but that will quickly evaporate as they move on to their next big exclusives coming. The indy game scene has basically continued focusing on whatever the best games it has in each genre until something comes out that finally beats it. People still talk about Shovel Knight, Minecraft, and Hollow Knight all these years later (not just players and companies, but gaming websites, giving them continued advertising constantly) because nothing had come out to beat those games in their fields, despite thousands of attempts. Sure, companies will hype up whatever they think the next big thing is, but when it fails to beat the indie Giants they rapidly move on to the next 4 person team working from a basement. It makes Hollow Knight getting to the top impressive, but it doesn't make its leg sales or continued being at the top seem impressive to me, because in my opinion, the Indy scene continues to freely advertise and highlight it's historically best games, which causes people like me to buy Hollow Knight or Minecraft years after everyone because of all those free references they receive years later by gaming websites, only to discover I didn't even play them much after purchasing.