It is no hidden fact that almost all natural resources on the planet are limited and non-renewable. When a government finally issues Population Control Policies, it's mostly because it is now having a hard time meeting the demand for resources the country has to offer.
Take for example Food supply: If there are 100million people in the country and the demand is 1kg/person/day and the maximum supply the government can offer is only 100Million kg/day. With population increasing exponentially, in the next year there will be an additional 5million +people. 105Million people = 100Million kg supply
By next year 5million people would starve daily since the demand is not met. This is what the government wants to prevent and is one of the main reason why they are trying to control over population to avoid scenarios like this. Another reason is:
A Controlled Number of Population also equals More Job Opportunities = Better Life
It gives support to growth and handles exponential expectancy. Again it enhances labour force and finally a means to control family thus creating some sort of joy and happiness.