It will be interesting to see what happens with Wolfenstein II, which as I understand it is a more demanding game than Doom. For all its tradeoffs, I'd still say Doom on Switch is a worthy conversion; hopefully the same can be said of Wolfenstein, but pulling it off is going to be a nightmare.
Yeah Breath of the Wild hit like a meteor strike, the hype was insane, and for most consumers getting the superior version on the trendy new platform was a much more appealing option than getting the inferior version on a dead system that was never cool.
Throw in Splatoon 2, Mario Odyssey, and other games that aren't quite killer apps but still add to the library, like Kingdom Battle, not to mention the upcoming Xenoblade 2, and you have a first year with vastly more appealing software than what Wii U had.
There's no mystery the way I see it; in the eyes of the mainstream consumer, Wii U had unappealing hardware and software and thus didn't sell, while Switch has appealing hardware and software, thus it's selling well.
Also this time Nintendo has good marketing and branding.