Because, as she grew old, she started to realize that her figure was becoming more and more resembling that of her father, who was chubby and short, unlike her slender mother. Even if cute and chubby children were more than welcome, and everyone would gladly scream 'how cute!' and croon over them, the same can't be said for when you were older yet still chubby.
So suddenly, Tian Wen found the path to achieving her dreams cut off. No matter how hard she and her parents tried, the most she could get was to act as small side character roles or passers-by or extras, who were there to just be show mascots or simple filler materials or background cannon fodder.
'But I'm not even that fat!' Tian Wen had cried out injustice in her mind, but who'd listen to her? She might only be a little chubby, but in the critical eyes of the casting directors, she was fat! Hence not suitable!
