I’ve thought about it, and while of course I’m sure many people have widely differing opinions as to why arcs resonate with them more or resonate with them less, I get the feeling that a big reason that the Skypiea arc may resonate with some people less relates to how nobody from Skypiea ends up joining Luffy and the others on the crew, and may result in feeling more distant in that respect despite the very interesting location and lore offered in it and world building resulting from that.
It’s a rather long arc that comes right after the semi-frequent streak of people joining as very close nakama one after another, and I suppose this was the arc that somewhat started to noticeably break up that streak. That may be partially why the Water 7 and Enies Lobby arcs had more power lended to them seeing as how they both basically focus on the personal character developments of Usopp, Robin, and Franky in particular, with Robin arguably feeling more distant from readers to begin with during the Skypiea arc in spite of her having helped out and her fight with Yama.
There’s character and tragedy explored with Noland and Kalgara’s past, though of course, they can’t join the crew and display a close kinship with the crew, a crew I’m sure many had grown quite attached to at this point otherwise, seeing as how they’ve both been dead for hundreds of years, which also gives a difference in regards to how distant some readers may feel they are from characters seeing as how previous told backstories usually took place about 10 to 20 years ago, as opposed to 400.
In regards to other people liking the Skypiea arc a lot and it resonating with them already, then it makes me wonder if people would like it even more and if it would resonate with them more had it played out that someone from the arc like Wyper had been focused on more on a personal level and had joined the crew.
If most of the New World arcs resonate with people less in the respect of Luffy’s crew not just having less main recruits, but also having less focus in general in the respect of raising more focus on the worldbuilding itself, then that would probably be a point relevant to here as well.