Don't lose heart that it's all based on profit. I imagine it's all to do with Sakurai's view on the reps. Waluigi I'm sure was considered but quickly discarded for a number of reasons, but he was given a (relatively) respectful role as an assist trophy. Whenever Sakurai goes out out of his way to say an assist trophy is not playable, I get the sense he knows the character has fans or that he himself is a fan. If he wanted to make the profitable choice, he would've put in every character who topped the polls, simple as.
Sakurai puts a value on surprise and the intrigue that creates. That's what the speculative community thrives upon. Waluigi was a known factor, much like Little Mac or MegaMan. I feel like, sadly, Waluigi wouldn't have surprised anyone, before Rosalina anyway, and actually divided some fans because his moveset can't be that astonishing. The other factor is uniqueness. Rosalina is almost an original character with how she uses her Luma, and this was effective in winning over fans who wanted Toad, Waluigi, Bowser Jr. and so on. These are only two factors of what must've been a hard decision for Sakurai. I can respect his choice when I step back and see that Waluigi is a fantastic character, but in terms of moveset potential he isn't as interesting as the Luma turned out to be, so Sakurai may have made the right choice for the sake of the game.
It still will bring a smile to my face whenever I see that assist trophy. It encapsulates what is Waluigi very well because of how it is short-lived and frantic. It gives a good idea of his personality and what his moveset would constitute. So I wouldn't lose faith in Sakurai, his reasons were valid, and there's always the next game when the competition is more slim.
I'd also like to thank you personally WAA for what you added to the thread, even just your post style was awesome. I hope that whoever makes the next Waluigi support thread gets someone as fun as you to brighten up the discussion.