It is uncertain exactly why, but naturally more boys are born than girls. Some scientific studies conclude that because male sperm (Y chromosome) is more active (but shorter lived) than female sperm (X chromosome) is the reason. Anyhow, the over evolutionary history this has proved advantage because men more often engage in more hazardous work and in armed conflict.
For whatever reason the # of boys born over girls born is only small difference. While it is true that many couples prefer boys over girls, that number is decreasing. Also when we factor in the natural birth distribution, the trend is OPTIMISTICALLY IMPROVING.
Furthermore, there are excess women in Russia, Japan, ASEAN, Europe, Americas, etc so the issue of finding a mate is a small issue in this globally mobilized world. And indeed many more Asian Males are getting married outside of their ethnic/racial group -- and this trend is positively increasing.
Lastly, this issue is often over-hyped in "certain" media (*cough* propaganda *cough*) outlets. You can see for yourselves there is a HEALTHY BALANCE of males-to-females in Asia (CJK + ASEAN). I am not certain of Pakistan, but I can speak for India. When I went to India it was SHOCKING to find an alarmingly greater gender imbalance -- much more so than in China, in fact terribly imbalanced. This is due to several important factors:
1) Pre-natal abortion
2) Post-natal "abortion"
Let's discuss the issue of post-natal abortion. This is when the baby has already been born. In India a greater bias towards males than females, leads to 2). What typically happens is one of several things:
a) baby girl is not fed for days or weeks, and left to starve to death;
OR
b) baby girl is suffocated with a blanket to die;
OR
c) baby girl is drowned in water to die
Bharat's situation is much more SEVERE than PRC for several important reasons:
Firstly, Hindustan's population density is unsustainable. In fact, it relies on MASSIVE IMPORTATION OF FOODSTUFF -- yet even with this there are massive starvations (leading to death) and farmer suicides each year!
Secondly, the gender imbalance in Hindustan is much, MUCH HIGHER. In the PRC the preference for boys is DECLINING, and there have already been talks to modify the preferred policy to 2-child as the population enters sustainable growth --- so this already becomes less of a future problem. In Hindustan however, little improvement (if any) have been accomplished. This problem is compounded when one considers Indian men have much harder difficulties attracting mates outside of their ethnic/racial group.
In conclusion, this issue has been highly hyped-up in PRC, while it has been glossed over in other more seriously affected regions of the world.