Bayonetta 3 is guaranteed for next year, it's BotW 2 that isn't.

Why would Bayonetta 3 be guaranteed but BotW 2 isn't when they both have the same amount of information regarding their release (2022)?

Bayonetta is just 2022, BotW 2 is aiming for 2022. I think that's a difference. The Zelda developers showed they're not 100% sure about it.

To be honest, I don't think any developer is 100% sure about the launch date until the game goes gold. I honestly think the fact that they even have a release window for the game, despite years of not telling us anything, means they are more confident than not. 

Switch is bound to slow down, it's gonna be north of 5 years.
But if all the releases come as expected and a few more unannounced gems - it's going to carry a lot of sales still.

I'm thinking around 20M give or take some should be a good target - With heavy hitters like Pokemon, Zelda, Mario + Rabbids, Monster Hunter, Splatoon and fan favorites like Kirby and Bayo.. it's bound to perform well still.

Unfortunately, it's almost a prerequisite for Zelda games to suffer at least one delay from their official announced release date.  I'm hoping that BOTW2 bucks the trend, though.

Voted for 22m-25m. I don't foresee a scenario where Switch sells less than 20m in 2022, even with chip shortages. They'll sell everything they ship, so I expect it to be pretty much flat with this year since I believe that there will be sufficient demand for it. I don't think we'll see Switch slow down next year with the OLED being such a sought after item and the software they plan to drop in 2022: BOTW2, Splatoon 3, Pokemon Legends Arceus (included for calendar, not fiscal), Rabbids, 3D Kirby, Bayo 3, Triangle Strategy, AW, Turtles... and that's just what we know. I don't think that saturation is going to greatly affect sales just yet.

It should drop next year but the question is how big will it be. After two 29 million years the DS only had a small drop to 27 million so it's possible something similar could happen for the Switch. I dunno how likely that is though so for now I'll go with 20-22m but I wouldn't be surprised if it does 23-25m either.

I think there are plenty of examples where that did not happen. Majora's Mask, Wind Waker, Spirit Tracks, A Link Between Worlds. I'm not saying it's not possible, but they have the world built, they have the assets done (for the most part). Unless there is a very large departure when it comes to the world I couldn't see how five years wouldn't be enough time for them. 

Worth noting that many people made that exact same argument for why it would launch in 2020 when it was announced in 2019. "It's the same map, same engine". That sure went well.

But I think it's more likely it will launch in 2022 than not.