if you are wondering why they got so popular, maybe simply because they had a different vibes from the rookies at that time? I also think that starship do a good job when creating and promoting their debut, like the photos and video teasers. I myself still thinks that IVE had the best group teaser (Have What We Want), and the member introduction videos (Show What I have). Their "Eleven" was also controversial because you either love or hate the tempo change (I myself got hooked by that part, and loved it).
Furthermore, some members had their viral moments, like that Leeseo's zoom cam, Liz's stable sings even when she cried, or Rei's gyaru pose. They also literally got two members (Yujin and Wonyoung) as the MCs of music shows. So it can be said that they are popular.
For the Love Dive anticipation, it was because people didn't know what kind of music that they would bring. And since Eleven got so many achievements, some dives kinda got worried if love dive turns out to be a bad song but alas, it got the same magic as Eleven. Even Love Dive was having a good fight against Still Life in the charts, despite their fandom power differences. Love Dive's magic was also shown when they were performing in the kpopflex and the huge crowd were singing the full chorus.
(I personally prefer Royal, because it shows more about the member's color, but I understand about why Love Dive is the chosen title track).
And for the GP appeal, it maybe because they had a good songs (for the GP taste) and viral moments.
(and maybe their concept too, because for some reason, there are many children and teens that love them and it makes their parent or guardian acknowledge them too).
Also, the thing that makes them standout is they are 5 month rookie at that time. So... yeah.
