To preface what I'm about to say, this isn't coming from a place of hate, but more of frustration. And this is just my personal opinion. Not saying this is by any means how he actually feels. What I feel is just based on my observations over time.
So now that that's out of the way, I wanted to pose the question; does Sakurai dislike/not care for the Donkey Kong franchise? I feel compelled to ask this question to get other perspectives, as I'm interested to see if others have ever felt this way. I'm a huge fan of the Donkey Kong Country franchise. It's my favorite video game franchise along with Super Smash Bros., so I'm obviously biased to the series. But with that said, my reasons for feeling this way are mostly attributed to the amount of content that has been included in each entry of the series. Donkey Kong has never gotten much representation. If you look at each game, the amount of content Donkey Kong has gotten pales in comparison to other franchises with similar popularity, if you look at things such as playable characters, stages, assist trophies, items, etc. I don't really count the content included from the original Donkey Kong arcade game, as I find that to be more of a Mario game than anything, as that game is not associated with the Country franchise, so I'll be leaving that content out (and even with that content, there still isn't much).
Melee - One playable character, three stages (two new, one from 64), one item.
Brawl - Two playable characters, two stages (one new, one from Melee), zero assist trophies, zero items.
Smash 4 Wii U - Two playable characters, two stages (one new, one from 64), zero assist trophies, zero items.
Ultimate - Three playable characters, three stages (none new), one assist trophy, zero items.
This is just a basic breakdown I made to better illustrate the lack of content Donkey Kong has had over the years. Donkey Kong is Nintendo's fourth best selling franchise (not including the Wii Fit series) behind Mario, Pokémon, and Zelda. When you look at the content Donkey Kong has received compared to these franchises, it doesn't even compare. Not to mention that smaller franchises such as Fire Emblem and Kid Icarus seem to get much more representation. The thing I find even more egregious about this is that even if you look at Ultimate with King K. Rool's inclusion, let's be honest; he was only added due to his immense popularity from the ballot. If not for the ballot, I don't think he would've been added even still, which means we still wouldn't have gotten any new Donkey Kong characters, even though Dixie Kong could've easily been added because of her inclusion in Tropical Freeze. And there are many other examples of lack of content outside of what I've listed (for example, only two music tracks from Tropical Freeze, both of which were already included in Smash 4). I say all this to say that I truly feel Sakurai either dislikes or has very little interest in the franchise, and it's frustrating as a fan. It's frustrating that such a big franchise is treated like such an irrelevant one. It's frustrating that with every entry in the series, we're expecting a new Fire Emblem character, but we're never realistically expecting a Donkey Kong character when one franchise is oversaturated and the other is almost entirely neglected. It's frustrating knowing that a very deserving character had to wait five games to get in and needed to help of a poll just to even be considered in the first place. Hell, I even thought it was crazy that it took Diddy Kong until Brawl to get in, as I felt he should've been a character in Melee, or at least should've at least been considered, which to my knowledge, he was never considered to be a character in Melee. And even in Brawl, I think it was originally planned that him and Dixie Kong would be a team character like Ice Climbers, as if Diddy Kong wasn't important enough to be a stand alone character.
To be clear, this isn't me calling for a boycott on Fire Emblem characters or anything like that. I just feel that the Donkey Kong franchise doesn't get the representation it deserves. It's just the lack of characters, the lack of stages and variety in them (every Donkey Kong stage is just a jungle...), etc. It even took until Ultimate for music tracks other than Jungle Hijinx being remixed like seven times to be included. It's just severely disappointing for me because I feel like there's so much great material they could take from the Country franchise, as it's a franchise that has so much to offer. I don't know if it's because the Country franchise is more popular in the West and has always been developed by foreign studios, and so maybe there's a lack of interest or familiarity there. Who knows. But any who, I didn't write this to rant or make anyone upset. I just wanted to open up the conversation, as I feel like it's an interesting one to have, given Donkey Kong's popularity compared to the amount of content included in the series.