Actually that's not really the case , and this is debunked by the following.
For Starters , World Tour was released the same month of Mario Kart 8.
Mario Kart 8 features a new set of clips for Rosalina by Laura Faye Smith , there's no 3D World voice clips in this game.
Footage of Rosalina voiced by Laura already existed way before the release month , which means voices were recorded way earlier ,which makes sense since it's usually that way with videogames.
This means , they could have used Laura in World Tour without problems but they ultimately gave it to Kerri Kane.
Even more , Laura as Rosalina debuted in 3D World which was in 2013.
They could have EASILY used those clips if for some reason the MK8 ones were not recorded by the time , which is unlikely.
The development argument does not really apply here either because Rosalina is not even in the base game , she was released later , giving them even more time to include the voice they wanted.
But , again they decided to use Kerri's voice.
During Smash , Rosalina was one of the first characters revealed , and in her trailer only Luma has a voice. She is silent.
However , it's they gave it to Kerri Kane again , which was highly likely a Development desicion , considering other newcomers have BRAND NEW voices.
This includes Palutena , Lucina , Robin , Corrin , Bayonetta , Ryu and etc.
Rosalina along with Jr are the only newcomers that do not have a voice for Smash , they have one reused from older games.
Further more , veterans like Kirby , Fox and Pit have NEW recorded voices. Hightlights on Pit because he changed voice actors , same goes with Sonic , his voice changed from Brawl to Wii U.
Rosalina , by this time , already changed voices , and yet they gave it to Kerri Kane instead of either using existing clips from Laura or having her record new Rosalina lines for Smash , like Sam Kelly did for Peach in Brawl because Jen Taylor was replaced by her.
All of this heavily implies this was a development desicion aka they prefered one over the other, not because they didn't have the clips.
And while Laura has been consistent during these past games , Kerri's voice is still featured as Rosalina in the Super Mario Line Stickers , which was way after Laura sticked around.
Lastly , Rosalina has been mute in her very few video appearences in the Sports SuperStars trailers.
They have only showcased Other characters , and they use their World Tour and Mario Tennis Open voices , which gives the vibe Rosalina will get her old voice too.
Im curious to find out.