Why? I mean, he has been an incredible producer for the series so far. I'm sure the new game will have lots and lots of new content, there's no wat they will use the same exact world again, and I trust Nintendo to understand how poor the controls and gameplay are in RDRII. If they take anything from the R* game, will be surely a more dense city areas or more random world encounters, or maybe a stronger narrative. But I'm sure the gameplay will be improved from BotW.
Because he's been heavily involved with Zelda for most of the series since it went 3D... And I'm not a fan of post-OoT Zelda outside of BotW - for instance, I see Wind Waker as a horrible Zelda game... Hot take, I know :p. I kinda enjoyed Twilight Princess on the Wii as a big launch title, but I don't have much of a desire to revisit it. And some of his ideas for the series strike me as really dumb and/or inconsistent for Zelda and its universe, e.g. the train in Spirit Tracks. That last part is the most worrying to me: I'm worried he might insert some random gimmicks or walk back on some of the things that made BotW the masterpiece it is, but obviously I'd love to be proven wrong.
I mean, it's pretty telling that it took them literally decades to realize that maybe, just maybe, the core of Zelda doesn't have to involve handholding the player through puzzles. I don't see BotW and its success as just a return to form or an exceptionally well-made entry, but as a wake-up call: 3D Zelda - as defined since OoT - has its audience, for sure, but it was stagnating with a formula that the general public didn't care much for in the end. If it did, the disappointing dungeons, fragmented puzzles, absence of handholding and deemphasized story would have angered most people and hampered the sales of the game. But it didn't, because it turns out that exploration, wonder and, to an extent, challenge are more quintessential to the Zelda experience. I hope Aonuma and his teams have taken that lesson to heart. Sidenote: it seems to be a theme with Nintendo in general, where they take their star franchises in weird directions for years before finally realizing they had it wrong, and it kinda annoys me after a while. See Metroid before Metroid Prime (and since Other M), or the fact that they waited almost 20 years to make a new 2D Mario game for home consoles. This, more than Aonuma himself, is what always makes me worried about Nintendo sequels. I'm never quite sure they'll be able to bring it home with sequels.
That said, I'm not quite clear on what Aonuma's influence is on each Zelda entry. Sometimes he's listed as producer, sometimes as director, and I don't know which position is more important in Japanese game development. For BotW, I was under the impression that Hidemaro Fujibayashi, as the director, carried most of the vision, even though Aonuma is in the limelight. Anyone knowledgeable on that topic? I'm genuinely curious.
