yeah it's hard to point to one specific thing but I think what
@Stilt Village is saying about bloatedness covers a lot of it. Odyssey and Pikmin 4 both have very "soft" endings where, once you roll credits, you're encouraged to just keep playing a bunch of new and remixed "post-game" content. it's a pretty straightforward process to actually play to 100% completion, something I never used to do in, say, Mario Sunshine or even Pikmin 2, and while it's fun, it ends up being a
lot of video game. and so on a replay you can go just for the credits and ignore the game's encouragement to keep playing for some much further-off secondary ending, or start to dig into the extra stuff but then feel like you didn't quite "finish" the game if you didn't do it all. i've started two or three new save files in Odyssey since I first 100%'d it, but I don't even have a strong memory of where I left off any of those later playthroughs.
there's some stuff specific to Pikmin 4 too—the other Pikmin games encourage you to replay to clear it in as few days as possible, but the fact that the night missions and some of the side content add to your day count end up making it feel pretty meaningless. the night missions in particular massively inflate the day count for any 100% run (and are also honestly quite tedious to do a bunch of back-to-back).
and while an upgrade system could be an interesting thing to strategize on, choosing the ideal upgrades based on how far in you are to maximize how much you could advance or something, in practice, they just made me feel like I had an incomplete moveset and underpowered Oatchi & Pikmin until pretty far in. the "canonical" way to play the game (especially the missions) feels like it only arrives once you're near the end. restarting from the beginning without all those upgrades (with the exception of the initial Pikmin deployment limit, which I think is a very smart idea) just doesn't sound all that fun. this may be my biggest issue overall—some recent Nintendo games just feel like you're not playing the "real" game from the start, and they're so big it's hard to feel motivated to start fresh.
anyway, I accept I'm probably way off here. I very nearly made a thread about this perceived phenomenon after SMB Wonder came out and only had one save file per Switch profile, and in general it feels like it does some of the things I'm describing, but I didn't feel like I could articulate it well or come up with clear examples, and I still feel that way! but I think there's something there. I probably first noticed it with Astral Chain, but it's also true with Splatoon's single-player campaigns and probably some others I'm not thinking of right now.