Nintendo very often announces ports and exclusives at their conference that aren't at the developers' conferences.
KH3 has been in development for years prior to Switch being announced, though the game would probably sell just as well as it would on the PS4, it's pretty late in the game's development for a Swithc port. EA has had a grudge against Nintendo since Nintendo offed EA from trying to make Nintendo's online store Origin back prior to WiiU's launch. Both the EA published indie developed games would likely sell best on the Switch (I mean one's a platformer, one of the Switch's bread and butter genres), so it's not a matter of EA not wanting Switch money. RDR2, Rockstar hasn't been a big Nintendo supporter in the past outside of the DS GTA game, some senior staff probably still have issues with what went down with Body Harvest on the N64. Other games could just be a case of developers not knowing how to optimize for the Switch given it's lower power than the XB1 and PS4. A title like say Just Cause 4 may not appear on it, but 3 had issues with optimization on the XB1 and PS4, so a Switch port may appear as a daunting task even though JC4 uses a new engine. I'd imagine that was the case with Far Cry 5, even though previous entries could be done on the Switch, 5's power draw may have meant a port with the limited Switch knowledge they had at that point would have been a tough task.
Wait until tomorrow to see, but they have massive "indie" support and strong Japanese support, the latter stronger than on the WiiU. The Switch has made some strides with the west with Bethesda supporting the system, Ubisoft usually has something going for it with multiplats and exclusives even if it's not a title like Far Cry 5, and engine support with UE4, Id Tech 6, Unity, and Snowdrop. Nintendo is also developing a new Switch engine that should help with third parties as they are making it to help them.