If I'm being honest, I put Xenoblade there mainly because i expect a rep in the second pass or further dlc but I still stand by with Kirby and dk. How are bandana dee and dixie kong not in yet?
Bandanna Waddle Dee is hard to say. Could it be because of somewhat Sakurai bias? He does favor the early era of games that he made. Nintendo might not see him as a key thing to put in Smash either, so DLC could be off the table.
Dixie is complicated. She was going to be a partner to Diddy Kong in Brawl, somewhat akin to Zelda/Sheik, Pokemon Trainer, and Samus/Zero Suit Samus. But it didn't work out, so whatever his combination ideas were, they had programming issues. He scrapped her from that game and gave Diddy(who overall is the bigger character of the two) the spotlight.
The complication is just how much he wants to stick to the partner idea. She's not in 4 or Ultimate, and in both cases, the partner idea would explain it well. Since that would require massive workload that they didn't have time for. She couldn't have been a last minute clone in 4 either, since she wasn't a regular costume, and she'd have been more difficult to do than Dr. Mario at best, since the moves aren't entirely there. She might've been a thought as an Echo for Ultimate, but she has enough unique abilities to think of going a different way. And she's not a clone or semi-clone in that game either. King K. Rool is a lot more simple than a partner idea, so that would make him an easier priority as is. Not just because he clearly did well in the ballot(some would argue the best set of votes too worldwide).
So you have a concept that's hard to implement since Brawl, clone/echo status that have various issues in making work right away, and a lower priority if you look closely as the intent behind the original character idea. He has yet to speak on her since the partner thing, so that's probably why overall.