Switch era Directs have consistently been in a Spring/Summer/Fall cycle, and we have yet to have the summer one.
I'd flip the question on it's head. Why make such a meaty Partner Showcase when that could have been packaged into a standard general Direct? The only two reasons I can think of are that they're either skipping the summer Direct entirely (which I do not buy, as there doesn't really seem to be a good strategic reason for doing so, especially with a bunch of announcements that should be happening imminently (Mario Kart tracks, Switch Sports update, Splatoon 3 testfire, etc.)) or because there's something unusual, like a hardware announcement, that's going to take a bunch of extra time in their presentation that would normally have been occupied by third party announcements.