Treyarch have actually always been really good with support for Nintendo systems- these are the folks who put Call of Duty 3 on the Wii at launch, then supported the Wii with all versions of their Call of Duty games (World at War, Black Ops), and even remastered and put Modern Warfare on the system. They had a version of Black Ops 2 ready for Wii U at launch.
All of which is to say, these folks put their games on Nintendo, so there was some expectation that maybe Black Ops 4 would be coming to the Switch. When a Switch version was omitted from the announcement, that hope became a bit foolish- and now, to clear the record on a Switch version of Black Ops 4 once and for all, Treyach senior producer Yale Miller has told Twinfinite explicitly, in as many words, with no potential for misunderstanding or misinterpretation, that no, there are no plans for a Switch version of Black Ops 4.
So that ends that- if you want to play Call of Duty this year, I recommend getting it on the other consoles (even the PC version will probably be dead this year, thanks to Battle.net exclusivity). Given that Black Ops 4 is multiplayer only, with no single player component, I guess this one kind of makes sense.