Probably because Lopunny has a Mega Evolution and Toxicroak and Floatzel don't. And Brock and Misty in SM got people hyped for returning characters getting Megas.
Brock's Croagunk may not have evolved but his Chansey, another happiness-based evolution and former Sinnoh cast member, did. Also, I think me and other people have mentioned this before, but the issue isn't with Buneary specifically so much as it is with Dawn being the only returning companion to not get any team changes or upgrades in her absence from the cast, and Buneary is only brought up so much because she and Quilava are the only two Pokemon on Dawn's team that can still evolve, and Buneary is brought up more because she was Dawn's first catch yet was so stagnant throughout her run as a main cast member that she never even completed her moveset, so people are logically gonna be overall more eager for her to get some sort of upgrade over Quilava. Though Ash having a Quilava of his own may also play a factor, since I think a lot of people would rather see Ash's Quilava evolve before Dawn's.
Because while Crogunk didn't evolve, Brock's Chansey actually did.
I really don't think that they'd care about Lopunny's reputation among the fandom. Not only because that didn't stop them from giving Mallow a Tsareena, but I don't think it would be an issue when Lopunny wouldn't have a ton of screentime. I'm also not sure about them being afraid to make major changes due to Ambipom's release. I know that western fans still complain about that decision, including myself, but I don't know if the reception was as bad or worse among Japanese fans. Even if that was the case, I don't know if they'd really be worried about that when most of those people, if not all of them, would be outside of the target demographic by now.
Sadly, that's probably at least a factor. Dawn's Piplup has always been marketable. It's still one of the most popular Water starters out there, so wanting to focus more on Piplup instead of doing more with Dawn's team would sadly fit.
Because Croagunk is a gag Pokemon and with few exceptions, they don't typically evolve. I also assumed that it's rivalry with Saturn's Toxicroak during DP also meant that it wouldn't want to evolve, even though they didn't specifically state that in the series. Croagunk not evolving isn't really a problem either since Brock's Chansey evolved into Blissey. It was still an upgrade for Brock's team and showed that he had made some progress off screen. It's a bit of a strange case though. Much like Buneary, Blissey is a friendship based evolution, but Dawn had been raising Buneary longer than Brock had Blissey. He raised it since it was an egg, but Dawn still had Buneary for a bit longer and it still hasn't evolved. It isn't unusual for Pokemon to just not evolve without a major reason. Croagunk and Buizel are good examples, but I think it's a lot harder to write Buneary off like that when it is a friendship based evolution. It was Dawn's first capture, so they've had plenty of time to strengthen their bond, especially after traveling through multiple regions. If Buneary needed a stone evolution like May's Skitty or something like that instead, then I think it would be easier to just hand wave away that it just doesn't want to evolve.
I don't see what makes Lopunny and Typhlosion not great fits for Contests, though? Nando himself used a Lopunny in the Grand Festival and the species in general is certainly a dead ringer for the elegance and grace that Contests are often associated with, and even then it's not like a Pokemon is required to be conventionally cute or pretty to excell at Contests anyway, since we've seen plenty of rather unorthodox species such as Banette, Swalot, and Pinsir being used to great effect. Heck, May herself was allowed to have a Blaziken, which is a species far more associated with conventional battles, and a Venusaur, which isn't typically considered to be all that cute or pretty. Compared to that, Dawn getting a Lopunny or a Typhlosion or even both seems fairly tame.
In what way? Nando had a Lopunny and May had a Blaziken and a Venusaur.
In addition to the responses people have already given, Croagunk's evolution would also undermine the rivalry it has with its evolved form (which as we just saw in the second episode of the special, the writers are still quite invested in) akin to Pikachu with Raichu.
The whole point of Contests though is to show the appeal and charm of any Pokémon though, rather than a stereotypical entry such as, say, a Milotic. Lopunny and Typhlosion are just as feasible as Buneary and Cyndaquil/Quilava. (I would suggest you check you Ruby from Pokémon Adventures, as his initial arc is breaking out of that mentality as a Coordinator).
How is Lopunny not elegant?
Wrong on both accounts.
I still think that both reasons there are kind of weak. There is a nice sentiment about Dawn wanting to keep her team and still work on making them all shine, but at the same time, it feels like such an unnecessary limitation for her. Unlike someone like Misty who specializes on one type and generally stays in one location, Dawn has been traveling around different regions to take part in Contests. The idea that Dawn has traveled through multiple regions off screen and didn't find a Pokemon she wanted to catch or considered trying to raise some new Pokemon to try out new routines is kind of unbelievable to me. I wouldn't expect her to catch a ton of Pokemon, but nothing new despite traveling through Johto, Hoenn and even Unova really does not make sense to me. It wouldn't be hard for her to rotate her team to try out new Pokemon.
You may think so, but that's what she decided on.
