Because the likelihood is, character reveals would be spaced out more for one franchise. Kirby had three playable reps in Brawl, two right from the start of development and Dedede was either the second or third new newcomer announced. Falco was one of the first known secret characters in Brawl and played a major role in the SSE, Wolf was one of the last characters added to the game (if not THE last) barring Sonic, and he was also one of the last characters unlocked, too.
A DK newcomer seems extremely likely at this point in time, and Diddy Kong was revealed very early on, way back in August. In Brawl, Diddy was one of the last starting newcomers announced and there was no other DK characters in the game.
Pit was one of the first confirmed characters for this game, and Palutena was announced this past E3, a year later. Lucario and Luigi were both announced very early on, despite both being secret characters in past games. Lucario is especially notable, as he was the second confirmed Pokemon character. We later got a dual reveal of Charizard and Greninja.
Frankly, if Krystal was in the game, I think either she would've been announced months ago, or Falco/Wolf would have. The fact that we're this late in development, this close to release, and we only have ONE Star Fox rep does NOT bode well for Krystal at all.
Maybe someone will try and argue "but Ike was only announced right before E3," but then I'll have to remind you that Marth (previously always an unlockable character) was announced last Fall, and six months later Ike was announced. Its been over a year since Fox was shown off at E3, and there's been no signs of a second Star Fox rep at all.
If we've had any additional Star Fox character announcements, I could buy the notion of a Star Fox newcomer in this game. I'd absolutely love to see Krystal, I think she'd work well (although I, again, think there's a lot of other characters who probably will, and should, get in before her), I really just don't see it happening and nothing hints at her at all.