I mean...not only was Wolf a derivative character (which, again, are characters that tend to be low priority, especially considering he was low priority even in Brawl), but Star Fox Command was the most recent Star Fox game that wasn't an upscaled port at the time development on Smash 4 started, and that was six years prior in 2006. That absolutely qualified as fairly irrelevant by that point.
So yeah, Wolf was:
1) From a series with waning relevance
2) Was, despite his changes, a derivative character, which have precedence for being low priority
3) Was almost dropped from Brawl because he was low priority even then
But also, again, Wolf was a veteran anyway. This statement is mostly about newcomers, as it stemmed from the idea of Tingle being added. When Wolf was actually added in Brawl? Yeah, he was very relevant, with Assault and Command still being well within the public conscience.