A Bonus character always seemed silly to me even as someone who was a believer in more DLC.
It's either it ends or we get another selection/Pass. Extending DLC for one character is silly from both Sakurai's and Nintendo's perspective.
I could see plenty of reasons.
- Third party company really super duper wants their character in Smash and straight up pays for development
- Nintendo sees a huge marketing opportunity for an upcoming title that fans would want to see in Smash. EX: SMRPG remake, so they add Geno as a fighter for fans, promotion, money, and advertising all in one!
- Character was cut into development and the team decided they really wanted to see their work added so they secretly worked on it until Sakurai approved it.
- They agree on 5 characters and someone realizes "Hey Kazooie is the only female in this, we need to fix that" so they make a couple extra female fighters as DLC to try to balance it out
- Something happened where the rights to a character could only be obtained if it wasn't sold as part of the fighter pass