Smash fans hate things that are cute/feminine? Since when has there been a negative reaction to Zelda's redesign?
I would figure that since Smash is a game about intense action that the slow paced life sim Animal Crossing is probably, on average, one of the least beloved Nintendo franchises among Smash fans. I consider myself a generally big Nintendo fan though I'll admit I care about their new stuff on average a lot less than I cared about their old stuff. I played the first Animal Crossing and thought it was boring which was a great reason for me not to play the rest of the series. If not for her role as an AT in Smash 4, I wouldn't know who Isabelle is. I would see her and think "some Animal Crossing character" but then not care too much beyond that, and I wouldn't know that K.K. Slider isn't the most important Animal Crossing character otherwise because in Smash he sure is (Saturday night performance!). It's not to say Isabelle doesn't "deserve" to be in; she probably deserves to be in about as much as Wii Fit Trainer... but she's also about as exciting to the average Smash fan.
Of course, you could just be a competitive like me and they're all gameplay functions anyway. In that case, this reveal is mostly a mystery since we really don't know how Isabelle plays. If things we haven't seen are really powerful and she's top tier, sure, I would happily play her. If she's bad, she might as well not be in, but that's also true for someone like Ridley even though he's really cool. I'm telling you that a competitive mindset sure makes this reveal cycle really easy; I recommend it! One of the many upsides is that it's actually impossible to be disappointed with the roster since I don't know which characters will be good but I sure know it will be some of them!