What's up with B-tier characters? They are supposedly very strong and should thus be played more, yet many of them seem somewhat uncommon. In this post I will hypothesize why that is. Most of this is speculation, so it should be taken with a grain of salt (most of this is based on my observations).
B:
Corrin (
): Corrin has a really good MU chart and really good theory, yet she is rarely seen at higher levels (and, from my understanding, she isn't all that common at lower levels either). I believe there are a few reasons for this: Firstly, she is DLC, and the last released character (together with Bayonetta). While Bayonetta gained popularity because she was (and still is) overpowered, Corrin had no such luck. Furthermore, Cloud basically has a similar MU chart that is better in many ways, and is also arguably easier to play (and Final Fantasy VII is a much more popular than Fire Emblem Fates, which might be a factor, especially at lower levels). Additionally, Marth and Lucina are also similar in many ways, and Marth is a Melee veteran who was very popular in Melee and still is popular at lower levels. Ultimately, I believe the strongest reason why Corrin is underplayed is that Cloud is simply better (oh, and losing to Diddy Kong, Fox, Sheik, and Cloud, even if they are just slight losses, is rather annoying if you're a top level player).
Lucina (
): Lucina (and Marth) have similar problems to Corrin. Unlike Corrin, Marth and Lucina seem to be very popular at lower levels. If I were to guess, I would place them in top 5 most popular in non-top level play, with Marth likely being more popular than Lucina. Anyway, Marth and Lucina were perceived to be underpowered at the release of the game, which likely reduced their potential playerbase. They eventually got buffed but by then many potential Marth/Lucina players had already moved on to other characters (this is speculation, but it seems plausible). Oh, but the biggest issue might, yet again, be Cloud. Why play Marth or Lucina when you can play Cloud? Regarding Marth and Lucina, they both have some reason why people might not want to play them. Marth: Spacing tippers can be hard, inconsistent, and frustrating. Lucina: Marth is generally believed to be better than Lucina, as are Corrin and Cloud.
Pikachu (
): Pikachu is considered by many secretly really, really good. Pikachu is also considered one of the most mechanically difficult character to play, which probably discourages many potential Pikachu mains. If you're willing to play a technical character who struggles to KO, why not play Sheik?
Meta Knight (
): Ironically enough, I believe Brawl is a major reason why Meta Knight isn't more popular than he is. When Smash 4 was released, Meta Knight wasn't very good in Smash 4, and going from Brawl Meta Knight to Smash 4 Meta Knight was likely frustrating, so many former Brawl Meta Knight mains moved on. He eventually got buffed, but then nerfed again. Why isn't he played more now, then? Well... This is speculation, but I think one of the reasons is that his gameplay is rather linear, which many top players might find boring (at least when using him as a main, he might be more appealing as a secondary).
Lucario (
): Have you seen Lucario's MU chart? It's kind of bad for a B-tier character (which makes me think Lucario should be C-tier, but I digress). Lucario can be stressful to play, since you rely so much on aura in order to win. Lose a stock early and you'll be behind. This stress factor combined with his overall not great MU chart probably turns many players away from Lucario.
Luigi (
): Big nerfs hurt, and he can also shares many of Mario's weaknesses (from my understanding), even if Mario and Luigi are very different in this game. The biggest reason, especially at lower levels, might be his down-B. Most players don't know how to mash it well and most don't want to learn how to. Oh, and his air speed is the second lowest in the game and he has the lowest traction in the game (which means that he glides a lot on the ground), which can be annoying when you're not used to it.
Captain Falcon (
): If I were to guess, I would say that Captain Falcon is one of the most popular characters in the game at lower levels. Why isn't he used more at higher levels, then? I believe the biggest reason is his MU chart, which leaves a lot to be desired. His playstyle is very different from most characters too, and not everyone might like that. Still, I think his biggest issue is his MU chart.
Peach (
): Peach is a very technical character who forces you to learn a whole new mechanic (floating) in order to do well. She's also
barely B-tier, which means that the rewards for learning such a technical character aren't that great.
What about C-tier? I think Olimar (
) and Greninja (
) have a good chance of being B-tier characters. Olimar got nerfed from Brawl and is a very strange character to play, which is probably one of the reasons why he isn't used more. As for Greninja, I'm not really sure why he's not used more. Too technical with not enough reward to justify using him over a top tier or Pikachu?