Military Wives-Babies

However, I'm honestly confused as to why there seems to be this huge stigma on once becoming a military wife, you are expected to just start popping out babies right away. And usually at a young age, before getting your education and or a career. One day I want a lot of babies, but after I have my degree and a steady job locked down. I get all of this pressure to have children while still being in my early 20s. 

I also understand that a lot of people have kids in their early twenties and some people say it's "just growing up" but there seems to be a tremendous amount of pressure from other wives, families, and military memebers for all of the wives to have babies, soon. 

Opinions as to why this is?