User blog comment:DerpyDoodle/Who is NEVER Going to be DLC?/@comment-1400578-20150409211537

Another thing to point out with the 4th-party characters is that while some of those you mentioned have been in video games, those have usually been fighting games, and Sakurai said that they would not be using fighting game characters in Smash since they wouldn't bring anything new to the gameplay.

http://nintendoeverything.com/why-sakurai-isnt-keen-on-adding-fighting-characters-to-smash-bros/