i think it might be her visuals. she's very skinny in a way that conforms to the beauty standards currently for models, if i'm not wrong. (also just a side note that wangyi is someone who struggles with trying to gain weight, as in she's trying but she can't really.) if she catches your attention enough to tune into her kdfj and zhibo, she's also very, very sweet which might make people who were originally there for her visuals stick around. imo it's still the CP though. there are people who might have paid attention initially due to the CP but ended up paying more attention to wangyi than zsy so they become her solos. or at least right now her CP is the biggest selling point so people might discover her via her CP activity but whether they like it / also like zsy after a while is a different thing. there's also a thing with popularity snowballing. right now wangyi ranks well (she is top2 afterall) which means by right she gets opportunities and screentime and lines and all of that which allows more people to discover her and become her fans. there might also be a portion of the fanbase who project on wangyi and assume her success as theirs, so they'd definitely be drawn to someone who is popular and considered successful

idk personally i guess i'm more of a wangyi solo than yzg rn because i don't have enough time to pay attention to zsy (since i mainly watch h2) but 4781 was definitely what drew my attention at first