Ah. So the 3 F-Zero games that have come out since Smash began all must have characters then.
No. It's a good reason.
F-Zero didn't do as well as other series included, its sales have dwindled since F-Zero X, regardless of how much I adore F-Zero GX, but they still got representation through the Port Town: Aero Dive stage from F-Zero GX and Captain Falcon is still the main character of those games, so his playable inclusion was representation enough..and lets be honest, aside from Samurai Goroh, not a lot of F-Zero characters lend themselves as naturally to Smash as other series' characters do. Not to mention that, outside of a few exceptions from primarily handheld series like Pokémon & Kirby, or games that only had new entries on handhelds like EarthBound and Kid Icarus, Smash Bros. usually places more focus on the console games than the handheld games, so F-Zero: GP Legend was unlikely..and F-Zero Climax even more-so considering it wasn't even released outside of Japan..and they were both more-so based on the anime and had poor critical reception to boot..not exactly the most likely contenders for Smash..
No, its really not. Fact is, Fire Emblem is one of Nintendo's bigger series these days, even if not up to Mario, Zelda, Pokémon, or Kirby levels, but likely more-so than most of the other series not released to one of those and it goes without saying that a new character would be likely for the newest entry in its series as none of the previous characters would represent the newest game as they are not main characters in it.
The problem with Fire Emblem isn't new characters like Corrin & Byleth, its old characters..and Chrom..since Marth has 3 clones, Ike is no longer relevant (aside from Heroes), and we don't really need three reps from Fire Emblem Awakening, especially when 2 of 3 are the aforementioned Marth Clones.
Pretty much what I'm saying is that rather than having all of these Fire Emblem characters continually returning and causing people to hate the newer characters that are more interesting than almost half of the current reps, it should be whittled down to just Marth, Robin, Corrin, & Byleth OR Marth, Ike, Robin, Corrin, & Byleth, plus a newcomer, as they are the more unique characters and 5 or 6 is a good enough number that isn't too many nor too few, representing several aspects of the FE series..and its still less reps than Mario (9 Reps), Pokémon (8/10 Reps), & Zelda (6 Reps).
Although it seems like its always a terrible idea, sometimes trimming the roster to include new content is the best way to go in order to avoid roster bloat, which is entirely what happened to Fire Emblem due to Everyone Is Here.
Please complain some. If no one here complains, some people assume it's because there are no complaints. This applies to more than character choices. The reality is that there are people who have stopped complaining and people who have left this forum.
Complaining is fine, when its reasonable..complaining every time a new Fire Emblem character is announced regardless of how they play but being fine with having all of the previous ones, half of which have the same moveset, return with no newcomers is not..thats when it seems more like just whining about something than anything else..
You forgot Squirtle and Ivysaur. They also had no technical reason to be cut in Smash 4 as ZSS came back.
My guess is that Sakurai didn't want there to be 8 Pokémon Reps taking up individual slots or something so he picked the most popular one out of the three..possibly wanting to keep the Mario series as the series with the most reps due to it being Nintendo's Mascot Series or possibly to keep the Pokémon Roster from being even more loaded with Gen 1 Reps.