Nope, it’s because they’re all from existing franchises that just so all happen to play a part in marketing a specific title. Corrin for Fates, Isabelle for AC 2019, and Incineroar for S&M.
Nobody hated Inklings not because they were expected but because they from a brand new IP, and people enjoy seeing new series represented in Smash and even though they’re recent characters that didn’t come from the 90s or 2000s, they were voted on the Ballot anyway, they just too recent in fact.
Most thought FE and Pokemon were too massively bloated at their times so when they added Corrin and Incineroar, Smash fans just saw them as mere shill picks that were only promoting a game.
Isabelle is a different case since AC only had one character but I’m guessing it’s either because they find her “cool” or if Villager was good enough.
Just my two cents.
EDIT: As for Wii Fit Trainer? Uh, I’m pretty sure that’s because she was chosen as a Shock unless you want to argue about Wii Fit’s sale when Sakurai never mentioned that.