I'd like to point out that people tend forget that a popular video game character and a Popular SMASH CHARACTER are TWO DIFFERENT THINGS. Just because a character is popular OUTSIDE of smash does not necessarily mean they will be a popular character IN smash and vice-versa.
Examples of the former is Capatain Falcon and Ice Climbers. Captain Falcon's games sold like crap both before and after his appearances in smash. Yet he is one of the most used and loved characters in Super Smash Bros. Most Falcon players i've known haven't even heard of F-Zero let alone actually played it. Also, no one before Melee heard of the game Ice Climbers and From what I heard, them and Mr. Game and Watch received almost as big a panning as corrin did because they weren't Wario or Diddy. But when they were Cut from 4 there was a huge outcry despite no one asking for them in melee in the first place.
Example of the Latter is Pac-Man who is the number 2 most famous video game character in the history of video game characters. Even my 82 year old grandma with Dimensia and who never played a Video game in her entire life knows who Pacman is. So of course fans were saying "He's a total icon so of course he should be in smash" but after he was included in smash he was generally treated as a red-headed step child. His trailer was met with a mellow "Oh, cool..." reception and now i almost never see a pacman player online and he is seldomly ever spoken of. People, like to bash Fire Emblem as being Niche but I can tell you now that I see alot more Fire Emblem characters online than I do Pacman.
Also, I get irritated when people say. Nintendo doesn't do what the fans want or what is popular in gaming. When Nintendo is popular BECAUSE they DON"T do what fans want or what's popular. How many mobs of people in 1985 were demanding a game where you play as a middle-aged italian plumber and you rescue a princess of toadstools from a giant turtle using a flower that let's you shoot fire? If Nintendo did what was popular, Mario would be a bald space marine that swore every 2 seconds and violently mowed down aliens with a machine gun. Splatoon is a modern example. If they asked fans what they wanted, we would have just got another, Golden-Eye/COD/Halo esq. First Person shooter.
Studio C did a reasonably good job of explaining how crazy the Idea of Mario actually is.
https://www.youtube.com/watch?v=IHC0nZSoOd4
What is great about Nintendo is that instead of giving you what you want, they give you what you didn't know you wanted.