I've said it before and I'll say it again the reason I think Dixie isn't talked about as much as say Bandana Dee is because their isn't a new DK game every other year the same way Kirby gets a new game every other year. Bandana Dee is overexposed because Kirby as a series is overexposed people will flock to whatever is new/shiny and shoved down their throats every 5 seconds. If Rare was still with Nintendo or if Retro wasn't slow as hell at making games (or when their other projects aren't cancelled) we would probably be receiving DK games on a regular basis instead of 1 game maybe every 5 years or so, which means more exposure to Dixie which in turn creates new fans and expands her fanbase.
I know what you're thinking "But that's not entirely true look at
or
they don't appear on a regular basis and were extremely popular and got in!" While you're right the thing with K.Rool and Banjo was that it was more than just making them playable in Smash. The fanbase was big because it was also a push/statement to Nintendo/Microsoft (in Banjo's case) that the fans don't want to see these characters fall into obscurity. K.Rool being added to Smash was mostly trying to tell Nintendo "Enough is enough! These one-off experimental villains aren't cutting it we want the OG back!" It was more about securing K.Rool a future in the DK franchise than just being playable in Smash. Banjo was the same it was more about showing Microsoft their is still a place in the gaming world for not only Banjo but 3D cartoony platformers on their consoles. They didn't want their franchise to completely die.
So with Dixie I feel she isn't as popular as she should be because like I said she isn't overly exposed as DK games don't come around very often, she rarely appears in major Mario spin-offs like Kart or Party and when she does appear in Kart its in the ****ty mobile game most of the world has moved on from playing. She also appeared in Tropical Freeze in 2014 despite not being in DK64 and Returns so their isnt this major push to "save this character" not to mention in Tropical Freeze she is treated like a glorified power-up and not a full playable character (unless you play hard mode which im sure less than 50% actually did) and that's where a lot of younger players know her from so in their minds their isn't much to work with. They don't/can't know the Dixie we know from DKC2/DKC3 because Nintendo refuses to put the DKC trilogy on SNES online to make it easily accessible to Switch gamers. Also with no new DK game in sight due to Retro working on Prime 4 their isn't much room for Dixie's fanbase to grow.
Also one other point Dixie isn't as popular as she honestly should be is that people seem to only care about 3rd party characters at this point. They are the dominant point of Smash speculation at the moment. Every 1st party character is considered "Safe and boring" by many unless you're Bandana Dee (mostly due to Japan) or Waluigi (because memes). I've seen people dismiss both Byleth and Min-Min as "boring 1st parties that should've been on the base roster or waited until Smash 6" as they see these 1st party characters as "wasted DLC slots that could've gone to my *insert my 3rd party character of choice here!*" Byleth got a lot of hate in particular but that's because people viewed him/her as just another "blue-haired anime FE swordsman to add to the already huge FE roster". Min-Min/ARMS character announcement on the other hand most people seemed luke warm on but eventually warmed up to once they played her/saw her in action. But she also was victim to "Ugghh another 1st party character!? Why do you keep adding Nintendo characters to your Nintendo published fighter about Nintendo characters fighting Nintendo!? WHY!? No one cares about ARMS!!" So if by miracle Dixie is one of the chosen Fighters pass 2 characters expect to hear a lot of the same moaning and complaining other 1st party DLC characters have gotten.