Maybe it's because she has a unique personality that people can relate to.
I think it's because she stands out from the typical manga characters. Her story is different and it makes people interested. Plus, her looks might be used to send a deeper message about acceptance and true beauty.
You might want to check out 'The Ugly Duckling's Journey'. It tells the story of a girl who was constantly underestimated for her looks but eventually blossoms into a beautiful and confident individual. The art style and plot development are really engaging.
The characters in the movie included the supporting character-Gu Mo, who had a cold personality and secretly helped Mo Qingge because she was on good terms with Su Ruolin. Male Lead-Nan Mingyu, The Royal Prince of Beauty| The Great Devil Who Makes People Fear| Cold and merciless in front of outsiders, unpredictable| To Mo Qingge, he was full of tenderness and affection.| Female Lead-Mo Qingge, Military Intelligence Bureau's Chief Executive| Holy Maiden Yun Ye, Princess Gulun| Drunken Fragrance Pavilion Master Rong Zihua & Ink Dye Pavilion Master Murong Moran| The most beautiful woman in the night| Pretending to be a pig to eat a tiger, male supporting character-Chu Liyun, Her Highness Li Wang of the Seal Country| Bitch and cowardly (Only in front of acquaintances, especially Mo Qingge)| Arrogant and cold in front of outsiders, full of royal style| Jiang Muyun|, male supporting role-Nan Zhu, the manager of the Drunken Fragrance Pavilion, Zhu Nan-fierce, decisive, ruthless| When I was a child, I met Mo Qingge in the military camp.| Real name Nan Zhu| To Mo Qingge, she was black-bellied and venomous, but also gentle and considerate.|, male supporting role-Mo Zijin, Mo Qingge's elder brother| He had doted on Mo Qingge since he was young.| However, he had been managing the military camp for Mo Yuanlang all year round and rarely returned to the residence.|, male partner-Mo Yuanlang, Marquis of Zhenbei| In order to get close to Su Ruolin| In order to gain military power, he framed the Su family and killed their entire family.|, male supporting role-Rongcheng, no relatives in this world, later taken in by Drunken Fragrance Pavilion| Because what he experienced was similar to what Mo Qingge experienced before she transmigrated, Mo Qingge thought of him as her younger brother.| His original name was Luo City, and his surname was changed to Rong|, male partner-Ye Fengyu, the third son of Guangling Ye family| Always dressed in white| like a scholar| handsome| Because Mo Qingge saved him, he joined the Ink Stained Pavilion.|, male partner-Chu Xiaoli, His Highness King Jing of Xi State| He looked gentle but was actually cold-blooded.| Treat human life as grass| To ascend to the throne, he would do anything to harm his brothers and sisters|, Supporting Female-Xin Lan, a first-class servant girl of the Northern Town Marquis's Estate.| One of Mo Qingge's confidants| Meager in thought, clean in action| Loyal to Mo Qingge| Respect Mo Qingge from the bottom of my heart|, female supporting role-Mo Qingyun, the eldest daughter of the concubine of the Marquis of Zhenbei.| Because he was jealous of Mo Qingge, he thought of ways to kill her.| femme fatale| In front of outsiders, she was graceful and elegant, like an elder sister.| The female supporting character, Yu Qiulan, was ruthless and unscrupulous in order to fight for the position of the matriarch. He killed the female protagonist's mother. Supporting Female Lead-Su Ruolin, Female Lead's Mother| The adopted daughter of the Empress Dowager, who was conferred the title of Eldest Princess and grew up with Emperor Yun Ye.| He's kind and gentle| She's the eldest wife of the Northguard Marquis.|. The Ugly Ugly Useless Woman's Peerless Beauty was written by Tan Moran. It was an ancient romance novel. [User recommendation: Mo Qingge would never have thought that the man she disliked at first sight was actually the scumbag who scolded her for being "stupid" when she fell into the water when she was young and then sat down to drink tea to watch?] One day, Nan Mingyu asked," "Little girl…do you really not remember this king?" Puzzled, Mo Qingge asked," "What do you mean?" Nan Mingyu patted Mo Qingge's head and said," "One year, you fell into a small lake in the fake mountain of the imperial palace…" Mo Qingge tried hard to recall and continued Nan Mingyu's words," "You saved me?" "This King is passing by…" "And then?" "And then…" "Wait…I remember…you're that scumbag! Damn tsundere!" . I hope you will like this book.
Maybe it's because such a unique character brings something different and makes the story more interesting.
You could check out 'Ugly Girl's Dream'. In this manga, the ugly girl has big dreams and works hard to achieve them, despite facing prejudice because of her appearance.
The reason could be to challenge traditional beauty standards or to create a character that has depth beyond her looks. Maybe the glasses and 'ugliness' are part of her character development.
One popular one could be 'Ugly Betty'. It shows the journey of an unconventional girl and has quite a fan base.
It could be a unique plot device to add complexity or drive the story in an unexpected direction.
One manga that comes to mind is 'Sailor Moon', which has many popular female characters.
The popularity of the manga's yellow girl could be due to her charming design. Maybe her outfits or hairstyle stand out. Plus, her character development throughout the story makes her relatable and interesting to fans.
It could be her unique personality, like being brave or kind. Maybe she has a cool look or some special powers.