Female children can be a burden in that a dowry is expected to be paid at a marriage in certain cultures and males might be expected to support the parents in certain cultures for another source of preference. There is also the culture that might prefer lineage to be passed down via males and some cultures prefer a male child to help in rural area manual labour around the home. These are mentioned in the article a bit - add to that the ability to determine the gender of a baby before birth and the ability to perform an abortion after determining gender and while technically against the rules in both nations, a gender based abortion will help create the gender imbalance. There's also a natural slight skew to having male babies among humans, it's much closer to 50/50 on conception but by birth it's not due to higher female mortality in the womb.
China actually has the opposite dowry problem: it's the male side that's expected to pay, and because of the skewed gender ratio, prices have risen. There are now families who don't want to have a son because they wouldn't be able to marry him off.
The assumption in this case would have been that the birth parents are made aware of the gender before birth and then are able to make a decision as to whether to abort and attempt for a male, or keep the female feotus.
why is this comment down voted by people? When I was born doctors were forbidden for reveal the gender of the baby. If anything I actually think one child policy helped the gender imbalance, before then, people could have how many ever children they want and abort how many ever baby girls they desired.