You mean like Kid Icarus, Punch-Out, and others? Seriously dead franchise isn't a good enough argument to count as a notch against getting characters. If that's the case how does Starfox have 3 characters while Metroid only got it's second in Brawl and people continue to argue that Ridley "is too big" even though it's a big franchise and actually had a game recently unlike Starfox.
Not really, I've no fondness for the man so your guess is as good as mine as to why he would chose to put in somebody like Wolf, make him a semiclone instead of a new character from a franchise that was still getting games at that point (Custom Robo DS) and Isaac as well with Dark Dawn, I just blame it on his horrible bias towards things he's worked on and maybe a lack of popularity. Coming up with a moveset for either is incredibly easy, also most of the characters you mentioned come from games with less than three games (which is what constitutes a franchise) barring Starfy.
Either way, you can't argue that they're unknown characters because FE didn't even exist here yet Roy and Marth made it through and allowed that franchise to actually come to the west.
"C-tier" franchises is also a poor example given punch-out, kid icarus, and I'd even throw in the supposed rhythm heaven in there. Should also include MOTHER considering the fact that the last game was for the GBA, it has little popularity in the US (even though it has a rather loud and obnoxious fanbase) and that series has two characters.