Diem
Agent of Phaaze
Not all of it is insincere, you're right, which is why I said "most." There are a handful of people I've seen or heard about who do have a genuine emotional connection to the character, as odd as that is.I mean, I don't think all of Waluigi's support is insincere. Yes, he wouldn't be where he is today in the West without internet memes, but I feel like his popularity was inevitable, moreso now that Daisy is in Smash. Aside from Toad, he's pretty much the only recurring major Super Mario character who isn't in Smash yet.
His support will come flooding back in the next game. Whether or not people will take him more seriously remains to be seen, but there isn't much more Sakurai can tap into unless generic enemies are the future of Smash.
Then there's my younger brother, who I don't think has ever played as Waluigi in any Mario game a day in his life (barely plays Mario games to begin with), who says he wants Waluigi in the game. Which is how most of Waluigi's support is, I have to imagine.