It is not that Wario was XXL is size that made him unattainable or the fact that Waluigi is always in the shadow of Luigi, but because no one ever thought to pair them up with a special lady.
Haters Gonna Hate
It turns out that this is because Nintendo’s Shigeru Miyamoto apparently didn’t want to imagine what they would look like on paper. You can read more about it in the embedded tweet below:
The reason Wario and Waluigi have no girlfriends, from a Nintendo Power interview with Hiroyuki Takahashi and Syugo Takahashi of Camelot. pic.twitter.com/n2cISa1klD
— Supper Mario Broth (@MarioBrothBlog) September 3, 2017