Just the one and only reason: Marketing
If you were with them since Day 1, (even before Produce 48), you would know they were always seen as equally pretty by korean beauty standars and everyone in general, both joined Starship around the same time, Yujin joined 2 moths before Wonyoung and Yujin's visuals were more popular, she is well known for looking like an actress and Starship saw more potential in her in the beggining, so she had lots of job's opprotunities as a model for sponsors and as an actress for music videos, she even worked with Cha Eunwoo (best male visual in kpop industry) before debuting, and already had a fanbase before Produce 48.
Sadly despite being a maknae too, she was never really seen nor treated as one by the public, she always looked "too mature" and was "too skilled"(which as someone who was always there with them as a fan, I can say I saw how many stans that were around same age as them, were always jealous of Yujin's skills and workethic, she literally has the record of the youngest participant ever in King of Masked singer, and would either ignore her or do very passive agressive comments towards anything she did, saying she "was trying hard to get the spotlight with her talents")unlike Wonyoung whose cute face makes her look younger than her real age and lacked skills, but was very cute and was a good english speaker, so she could be "the 2nd Somi", so her "child image" suited her a lot, and was very relatable for preteens and young students with average lifes since she talked a lot about her school and academic achievements, unlike Yujin who talked more about her life as an idol (which as a young girl, other teens would watch it and get jealous of her beavuse they dont find her relatable)
17yo Wonyoung:
17yo Yujin:
(It doesnt which pic you use, Yujin always looks her real age or older, more mature and Wonyoung looks like a 13yo for heer baby face and feautures)
Young maknaes always have existed but none of them as successful as Wonyoung, because most young maknaes already look "too old" (Yujin) or are "too skilled" (Yujin) so people sometimes forget they are maknaes too and "lose the charm of getting beloved and popular easily", NI-KI from Enhypen and back then I-land is the perfect example, he was only 14, but looked and acted older than his real age with all his exprience as a dancer, other trainees saw him as threat for being a dance prodigy that had already achieved so many things as a kid (was Shinee backup dancer, passed an audition for Michael Jackson's coreographer when he was 9yo).
So with this I hope I explained well how their totally different images were built through their 4 years of career, Yujin having a more professional, mature, and threatening image to insecure mfs out there that cant help but see a young girl doing better at her career and being more professional than how their lazy existence will ever do.
While Wonyoung is "the nation grandaughter" who has a lot of “grandma” or even “unnie” fans from when her honeybee fancam went viral. she has a “younger sister” or “daughter” image in korea which can be seen with how her saying “ungnie” which is just a cuter way to say “unnie” went viral on k-twt here.
Yujin image and reputation is less appealing, more intimidating and easily makes others insecure, so she is less popular.
New kpop stans arent jealous of Wonyoung real self, they are just jealous of who they think Wonyoung is, old kpopstans arent really jealous of Wonyoung, unlike new kpop fans, since they see her in totally different ways, as an old fan I never really expected she could get envied, Yujin was always the one kpop lazy fans were jealous of, she is just so profesisonal at what she does that anybody could find her intimidating and feel insecure.
Some old fans take some much pride on not getting jealous of Wonyoung since they know who she really is, so they love defending her and telling othr that false idea they have of Wnoyoung is real and they are just jealous and insecure of her while they arent(I mean exactly, her fans arent jealous of her because they know she is mid, and that is the reason they like her so much, she doesnt make them feel insecure, because she is not even that pretty unlike other idols like Tzuyu and Minju, while new kpop fans who just joined kpop world in 4th gen think she is IT, because they always see comments and posts overpraising her that they dont relaize it is overpraising, they just think it is truth that she is IT so they are jealous).
The best example for this is her visuals, they always say "you are just mad and jealous she is so unreal, ethereal the prettiest and most perfect girl in the world and you are ugly", Wonyoung is very cute but if you are an old fan that has been with them since the begginning, you know she isnt a visual and she even used to get bullied by knetizens for her looks, saying she was ugly in real life and makeup makes miracles with her, that she had ugly eyes, a rectangle body shape with no hips or defined waist, an ugly nose or that her cheeks were too fat.
She doesnt really fit koren standars, but in Korea sometimes charm is more important than being actually pretty, like Jennie from Blackpink who is well know for being sexy and her badass image, but kenitzens bully her saying she has an ugly nose, ugly chin or that her cheeks are too fat.
so as an old fan it is werid for me when I see everyone saying they feel insecure when they see Wonyoung beacuse she is insanely beautiful... like I would have expected it from Minju, not from Wonyoung, but unlike me most of her old fans enjoy and contribute with this new fake image of her since they pity her, similar to Brave Girls, everyone loves you and puts you on a pedestal if they see getting attention you had never gotten before and keep using it, as a way to make her haters mad, but inside the only reason they arent jelaous of her it is because they dont really see her as her haters ee her.
I personally find celebrities like her a little weird, she is like korean Sakura Miyawaki, like if you dont know her story you either really think people put her on pedestal for exisitng when she is not even very pretty nor talented (if everything was related to beauty or talent, Minju, Hyewon and Chaeyeon would be insanely popular), or you really start believing all the overpraising she gets from her fandom that is already there, so you become a fan too and go with the flow, in Sakura's case her story is a little odd since she has lots of scandals, but still her photoshoots sell better than gg albums, but I wasnt there as a fan of hers when her career started so I dont know.
