breath of the wild 2 gets a name, release date, at the next nintendo direct. it launches with switch revision in the summer, prior to or around e3.
smg2: revealed at e3 2009, release date in february 2010, released in may/june (sorry eu) 2010
botw2: revealed at e3 2019, release date in jan/feb 2020, released in may/june 2020
regarding strategy it's this: do you want to wait and get a new system months from now *or* do you want a shiny new system now, with a brand new awesome game? botw2 will still be on the switch during the holiday season.
super mario game is their major holiday title. it plays better with families during the holiday season and there should be something that's not just a port for mario's 35th year. they treated super mario maker with a good deal of respect as the 30th anniversary game and super mario all-stars and super mario galaxy 2 on wii was their way of doing a 25th anniversary. pretty sure botw would have been given a 30th anniversary treatment on switch had it launched in 2016 as originally planned.