Surely this is irrelevant to the fact that Daisy can't make it into a main series game, is getting snubbed even on spin-offs, isn't queen of anything relevant, doesn't have an army like Rosalina does, has little to no backstory, etc. But I'll answer anyway.

Not even sure why this is a point considering it makes her faster than Daisy, though. The Mario Kart bio says that she's heavy because she's made of heavy elements from Grand Stars and such. Something ELSE she has on Daisy. When will Daisy be relevant enough to be made from Grand Star elements? Though the funnier part is that Rosalina is lighter than Peach in smash, which, by default, makes her lighter than Daisy if she were to be in smash considering we all know she'd be a Peach clone.

Better question is why would she have one? She has no personality, no game to sell, no place in Smash, wouldn't even make an interesting Yarn Yoshi skin...

that may be so but Daisy has the comfort of knowing that she's not a potential mascot for the next entry in the 'Wii Fit' series

She can take comfort in the fact that she won't be a mascot for anything nor will she have exposure anywhere.