Ports don't need to sell 5 million. The Wii COD games sold 1-2 million and yet were profitable enough for them to keep coming year after year.
Doom 2016 sold less than a million on Switch yet was profitable enough for Doom Eternal to be ported.
So what’s the reason then?
With COD, Activision doesn’t manage the same volume of sales as the ones you mentioned.
Every COD game on PS4 crossed the 5 million mark easily in a couple of months and I reckon that most COD’s on PS4 already crossed the 10 million mark.
Why they would spent money to port COD to switch only to sell 1-2 million units LTD when they can sell that quantity on PS4/Xbone/PC in a couple of weeks??