I think there's two different things going on here. First as far as the lack of Nintendo IPs, I suspect development has shifted to the next gen console and we'll be moving on from the Switch soon (I predict next year is when the new console will launch, but it could also be 2025). So we're not seeing many games because most of Nintendo's studios are working on next gen launch titles. This is almost certainly the case with the Mario Kart team and Mario team in particular, which haven't really done much since 2017, it feels time for new entries in those IPs but those IPs would have more impact early in the next console's life than late in the Switch's life. But beyond that there's a couple of other rumored games and games that feel like they might have something to show simply due to the amount of time since the last entry (DK, Yoshi, Luigi's Mansion, 2D Zelda) and yet we have nothing but DLC confirmed for after Pikmin 4, so again this is all probably being held for next gen. As for Baseball specifically, I'm not sure it exists, it might be a bit soon for it since we had Mario Golf: Super Rush in 2021 and Next Level Games releasing Mario Strikers: Battle League just last year, so I'm not sure they really have something for this year. They might be working on the next gen Mario Tennis game.
As far as the lack of NSO, I think it's because they want to add Home support and that might be delaying things. Pokemon fans get very upset when they can't transfer their Pokemon to newer games (see: the lack of connectivity between Gens 2 and 3, Dexit), so they're going to want a way for players to transfer Pokemon from the NSO titles to Home (and a way to transfer them from the GB games to the Stadium games). It's possible they're running into troubles getting NSO to work with Home so they're not ready to confirm the main games are coming.