Everyone keeps bringing up Mario Run, but what about Pokémon Go? It's Nintendo's biggest IP and it's absolutely multiplatform, particularly as it's available on the main competitors for a Switch user's time i.e. mobile phones/handhelds. They continue to lease/develop content for it and it had generated 6b of revenue by 2020.
Nintendo is never going back to being a single-ecosystem-exclusive developer because they struck gold with multiplat. They're not pushing Mario Odyssey to PS3/Vita because the market's not there, the game isn't suited for that demographic, and they know they need exclusives to justify their hardware's existence given the appalling and chronic lack of third party support.