Name a third party game that has sold more than 5 million on another system that actually got a fully featured version of the game on Switch released at the same time.

Pretty sure there isn't a single one.

AAA third party sales aren't bad on Switch, there just are zero new AAA third party games on Switch. Everything it has gotten is released years late which obviously aren't going to sell crazy numbers, or with something like Fifa they put out an inferior different version on Switch which certainly isn't gonna endear gamers to pick it up even if they do want a Soccer game on Switch because its basically a slap in the face.

So it's not because of power, it's not because of sales. It's probably just because they mass produce iterations of CoD games annually so it's probably just easier to make the same game each year with you know different settings and whatnot than have to make two different versions of it each year. They've turned CoD into a factory line game where fans will just keep buying the same game, but they need development to be as efficient as possible to keep this factory line up. And they've probably found in the past that making an extra version for Nintendo's lower hardware specs makes this cookie cutter process less efficient.

COD doesn't push PS/Xbox either, it's 60fps on even the base consoles and less demanding than 30fps games like Witcher 3 or Hellblade.

Companies don't always make the right decision. Sometimes they can be shortsighted.

How much COD sells on PS4 is irrelevant, COD's already there and getting one of the many external porting studios to bring them to Switch would take nothing away from that. With even 1 million sales per game, that's a ton of extra money you otherwise wouldn't have, and more money and always better than less.

Again, Doom sold under a million on Switch but it was still evidently profitable enough for Doom Eternal to be greenlit for the platform.