This is what most of the Waluigi support amounts to. Compared to fanbases like with Ridley and K. Rool, who people are seriously invested in, Waluigi's support is just because people think he's a funny character and that they're funny by liking/playing as him.
Last year during Nintendo's Summer of Play event, I went to the mall to go get my hands on the Switch (this was back when they were hard to find). A friend and I played a Mario Kart 8 Deluxe game with two other strangers. One of them picked Waluigi, thought it was so funny, and was a shrill, screaming manchild the entire game. I was playing as Link, won the game, and then he kept screaming "WHO WAS LINK?! WHO WAS LINK?!" like it was hilarious. And he was probably older than I was.
Not that I'm generalizing every single person who wants the character. Not every Waluigi fan is shrill and immature, of course. There are some people who genuinely like him and would seriously play him, but they're definitely the minority.
If he does ever get added, it will probably be funny for a month, give or take, and then everyone will go home.