>>/150749/
Lots of reasons
One major reason is to look more childlike or delicate, I think that's the case with Pukara along with her desire to look like a korean or japanese idol, however those girls use makeup and filters to hide the gaunt sickly appearance that comes with being malnourished 
This shit will only do her more harm in the long run as not eating enough can make you age faster (ironic isn't it?)